fix windows EOL in markdown files

[agrandville]

zola v0.15.3
os windows

if ```linenos is enable in codeblock and EOL is windows style (0xD,0x0A) vs unix style (0x0A),
code highlighting failed.

Text are borrowed, to sanitize the CR+LF to LF, the strings are split in parts.
To reconstruct the string, parts must be concatenated.
cf pulldown-cmark/pulldown-cmark#507

check

> cargo test  --test=codeblocks --package=markdown
running 21 tests
test can_add_line_numbers_windows_eol ... ok
test can_add_line_numbers_with_lineno_start ... ok
test can_add_line_numbers_with_highlight ... ok
test can_add_line_numbers ... ok
test can_highlight_all_lines ... ok
test can_hide_lines ... ok
test can_highlight_at_end ... ok
test can_highlight_line_range ... ok
test can_highlight_out_of_bounds ... ok
test can_highlight_mix_line_ranges ... ok
test can_highlight_ranges_overlap ... ok
test can_highlight_reversed_range ... ok
test can_highlight_single_line ... ok
test can_highlight_single_line_range ... ok
test can_highlight_unknown_lang ... ok
test can_highlight_weird_fence_tokens ... ok
test can_render_multiple_shortcodes_in_codeblock ... ok
test can_highlight_zero_start_same_as_one ... ok
test does_nothing_with_highlighting_disabled ... ok
test can_render_shortcode_in_codeblock ... ok
test can_render_completely_mixed_codeblock ... ok

test result: ok. 21 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.57s

[Keats]

Thanks!