Add documentation about all cross-platform terminal characters

[ehmicky]

I have run some code to print all Unicode codepoints from U-0000 to U-10fff on:

• Ubuntu 20.10, Gnome terminal
• macOS, default terminal
• Windows 10, cmd.exe, CP850

The following characters appear to be the full list of characters correctly displayed in all of those environments:

0000-058f (most)
1d00-1fff (most)

2588 2593 2592 2591 2580 2584 25ac 25a0 25aa 25a1 25ab 258c 2590
█ ██ ▓ ▓▓ ▒ ▒▒ ░ ░░ ▀ ▀▀ ▄ ▄▄ ▬ ▬▬ ■ ■■ ▪ ▪▪ □ □□ ▫ ▫▫ ▌ ▌▌ ▐ ▐▐
  ██   ▓▓   ▒▒   ░░   ▀▀   ▄▄   ▬▬   ■■   ▪▪   □□   ▫▫   ▌▌   ▐▐

2500 2012 2014 2015 203e 2501 2550
─    ‒    —    ―    ‾    ━    ═
2504 2505 2508 2509 254c 254d 2212 2574 2013 2010 2578 2576 2043 257a 257c 257e
┄    ┅    ┈    ┉    ╌    ╍    −    ╴    –    ‐    ╸    ╶    ⁃    ╺    ╼    ╾
┄┄   ┅┅   ┈┈   ┉┉   ╌╌   ╍╍   −−   ╴╴   ––   ‐‐   ╸╸   ╶╶   ⁃⁃   ╺╺   ╼╼   ╾╾
2502 2503 2551 2016 2506 2507 250a 205e 250b 254e 254f 2575 2579 2577 257b 257d 257f
││   ┃┃   ║║   ‖‖   ┆┆   ┇┇   ┊┊   ⁞⁞   ┋┋   ╎╎   ╏╏   ╵╵   ╹╹   ╷╷   ╻╻   ╽╽   ╿╿
 │    ┃    ║    ‖    ┆    ┇    ┊    ⁞    ┋    ╎    ╏    ╵    ╹    ╷    ╻    ╽    ╿
250c 256d 250f 250d 250e 2554 2552 2553
┌    ╭    ┏    ┍    ┎    ╔    ╒    ╓
2510 256e 2513 2511 2512 2557 2555 2556
┐    ╮    ┓    ┑    ┒    ╗    ╕    ╖
2514 2570 2517 2515 2516 255a 2558 2559
└    ╰    ┗    ┕    ┖    ╚    ╘    ╙
2518 256f 251b 2519 251a 255d 255b 255c
┘    ╯    ┛    ┙    ┚    ╝    ╛    ╜
251c 2523 251d 251e 251f 2520 2521 2522 2560 255e 255f
├    ┣    ┝    ┞    ┟    ┠    ┡    ┢    ╠    ╞    ╟
2524 252b 2525 2526 2527 2528 2529 252a 2563 2561 2562
┤    ┫    ┥    ┦    ┧    ┨    ┩    ┪    ╣    ╡    ╢
252c 2533 252d 252e 252f 2530 2531 2532 2566 2564 2565
┬    ┳    ┭    ┮    ┯    ┰    ┱    ┲    ╦    ╤    ╥
2534 253b 2535 2536 2537 2538 2539 253a 2569 2567 2568
┴    ┻    ┵    ┶    ┷    ┸    ┹    ┺    ╩    ╧    ╨
253c 254b 253d 253e 253f 2540 2541 2542 2543 2544 2545 2546 2547 2548 2549 254a
┼    ╋    ┽    ┾    ┿    ╀    ╁    ╂    ╃    ╄    ╅    ╆    ╇    ╈    ╉    ╊
256c 256a 256b
╬    ╪    ╫
2573 2572 2571 2044 2215
╳    ╲     ╱    ⁄    ∕
      ╲   ╱    ⁄    ∕

2024 2219 2022 25e6 25cb 25cc 25cf
․    ∙    •    ◦    ○    ◌    ●
25b2 25b4 25b8 25ba 25bc 25be 25c2 25c4
▲    ▴    ▸    ►    ▼    ▾    ◂    ◄
2190 2191 2192 2193 2194 2195
←    ↑    →    ↓    ↔    ↕
2302 25ca 25d8 25d9
⌂    ◊    ◘    ◙

2018 2019 201a 201b 201c 201d 201e 201f 2032 2033 2e17 2039 203a
‘    ’    ‚    ‛    “    ”    „    ‟    ′    ″    ⸗    ‹    ›
2026 2030 203c 203d
…    ‰    ‼    ‽

2248 2260 2261 2264 2265
≈    ≠    ≡    ≤    ≥
2202 2206 220f 2211 221a 221e 221f 2229 222b 2310 2320 2321
∂    ∆    ∏    ∑    √    ∞    ∟    ∩    ∫    ⌐    ⌠    ⌡
2153 2154 2155 2156 2157 2158 2159 215a 215b 215c 215d 215e
⅓    ⅔    ⅕    ⅖    ⅗    ⅘    ⅙    ⅚    ⅛    ⅜    ⅝    ⅞
2070 2071 2074 2075 2076 2077 2078 2079 207a 207b 207c 207d 207e 207f
⁰    ⁱ    ⁴    ⁵    ⁶    ⁷    ⁸    ⁹    ⁺    ⁻    ⁼    ⁽    ⁾    ⁿ
2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 208a 208b 208c 208d 208e
₀    ₁    ₂    ₃    ₄    ₅    ₆    ₇    ₈    ₉    ₊    ₋    ₌    ₍    ₎
2090 2091 2092 2093 2094
ₐ    ₑ    ₒ    ₓ    ₔ

2020 2021 263a 263b 263c 2736 2640 2642 2660 2663 2665 2666 266a 266b 266f
†    ‡    ☺    ☻    ☼    ✶    ♀    ♂    ♠    ♣    ♥    ♦    ♪    ♫    ♯
2105 2113 2116 2117 2122 2126 212e 2132 214d 214e 2183 2184
℅    ℓ    №    ℗    ™    Ω    ℮    Ⅎ    ⅍    ⅎ    Ↄ    ↄ
20a0 20a1 20a2 20a3 20a4 20a5 20a6 20a7 20a8 20a9 20aa 20ab 20ac 20ad 20ae 20af
₠    ₡    ₢    ₣    ₤    ₥    ₦    ₧    ₨    ₩    ₪    ₫    €    ₭    ₮    ₯
20b0 20b1 20b2 20b3 20b4 20b5 20b6 20b7 20b8 20b9 20ba 20bd 20bf 0e3f
₰    ₱    ₲    ₳    ₴    ₵    ₶    ₷    ₸    ₹    ₺    ₽    ₿    ฿
2460 2461 2462 2463 2464 2465 2466 2467 2468 2469 246a 246b 246c 246d 246e 246f
①    ②    ③    ④    ⑤    ⑥    ⑦    ⑧    ⑨    ⑩    ⑪    ⑫    ⑬    ⑭    ⑮    ⑯
2470 2471 2472 2473 24ea 24ef 24f0 24f1 24f2 24f3 24f4
⑰    ⑱    ⑲    ⑳    ⓪    ⓯    ⓰    ⓱    ⓲    ⓳    ⓴
24ff 2776 2777 2778 2779 277a 277b 277c 277d 277e 277f
⓿    ❶    ❷    ❸    ❹    ❺    ❻    ❼    ❽    ❾    ❿

2c60 2c61 2c62 2c63 2c64 2c65 2c66 2c67 2c68 2c69 2c6a 2c6b 2c6c 2c6d 2c6e 2c6f
Ⱡ    ⱡ    Ɫ    Ᵽ    Ɽ    ⱥ    ⱦ    Ⱨ    ⱨ    Ⱪ    ⱪ    Ⱬ    ⱬ    Ɑ    Ɱ    Ɐ
2c70 2c71 2c72 2c73 2c74 2c75 2c76 2c77 2c78 2c79 2c7a 2c7b 2c7c 2c7d 2c7e 2c7f
Ɒ    ⱱ    Ⱳ    ⱳ    ⱴ    Ⱶ    ⱶ    ⱷ    ⱸ    ⱹ    ⱺ    ⱻ    ⱼ    ⱽ    Ȿ    Ɀ
a717 a718 a719 a71a a71b a71c a71d a71e a71f a720 a721
ꜗ    ꜘ    ꜙ    ꜚ    ꜛ    ꜜ    ꜝ    ꜞ    ꜟ    ꜠    ꜡
a788 a789 a78a a78b a78c
ꞈ    ꞉    ꞊    Ꞌ    ꞌ
fb00 fb01 fb02 fb03 fb04 fb05 fb06
ff    fi    fl    ffi    ffl    ſt    st
fb13 fb14 fb15 fb16 fb17
ﬓ    ﬔ    ﬕ    ﬖ    ﬗ

Adding all of those would probably reduce the usability of this library by adding lots of useless characters.

However, I believe there might be some useful characters that could be added. I have opened #52, #53, #54, #55, #56, #57 for those. If there are some others you think might be interested that are not covered by those issues, please let me know and we can add issues for them. 👍

However, it might still be useful for some users to know the full extent of available cross-platform terminal characters. To do this, I am considering creating a repository with the symbols above, and link it at the end of this library's readme.md. Do you think this would be useful?

[sindresorhus]

However, it might still be useful for some users to know the full extent of available cross-platform terminal characters. To do this, I am considering creating a repository with the symbols above, and link it at the end of this library's readme.md. Do you think this would be useful?

Yeah, I think that could be useful.

[ehmicky]

Done in #68.