Add hex color support

[TutenStain]

This PR adds support for parsing hex colors, based on discussion in issue #65

Feel free to suggest changes. My first few lines in Rust.

[fcsonline]

Welcome to Rust! And welcome to tmux-thumbs too! 👏

Awesome to add hex colors support for tmux-thumbs!

I suggest doing these changes to ensure better that the incoming format is a good one:

diff --git a/src/colors.rs b/src/colors.rs
index 7042286..96a3d46 100644
--- a/src/colors.rs
+++ b/src/colors.rs
@@ -1,13 +1,18 @@
 use termion::color;
+use regex::Regex;
 
 pub fn get_color(color_name: &str) -> Box<dyn color::Color> {
+  let rgb = Regex::new(r"#([[:xdigit:]]{2})([[:xdigit:]]{2})([[:xdigit:]]{2})").unwrap();
+
+  if let Some(captures) = rgb.captures(color_name) {
+    let r = u8::from_str_radix(captures.get(1).unwrap().as_str(), 16).unwrap();
+    let g = u8::from_str_radix(captures.get(2).unwrap().as_str(), 16).unwrap();
+    let b = u8::from_str_radix(captures.get(3).unwrap().as_str(), 16).unwrap();
+
+    return Box::new(color::Rgb(r, g, b));
+  }
+
   match color_name {
-    color_name if color_name.starts_with('#') && color_name.len() == 7 => {
-      let r = u8::from_str_radix(&color_name[1..3], 16).unwrap();
-      let g = u8::from_str_radix(&color_name[3..5], 16).unwrap();
-      let b = u8::from_str_radix(&color_name[5..7], 16).unwrap();
-      Box::new(color::Rgb(r, g, b))
-    },
     "black" => Box::new(color::Black),
     "red" => Box::new(color::Red),
     "green" => Box::new(color::Green),
@@ -35,12 +40,18 @@ mod tests {
 
   #[test]
   fn parse_rgb() {
-    let text1 = println!("{}{}", color::Fg(&*get_color("#1b1cbf")), "foo");
+    let text1 = println!("{}{}", color::Fg(&*get_color("#1b1cBF")), "foo");
     let text2 = println!("{}{}", color::Fg(color::Rgb(27, 28, 191)), "foo");
 
     assert_eq!(text1, text2);
   }
 
+  #[test]
+  #[should_panic]
+  fn parse_invalid_rgb() {
+    println!("{}{}", color::Fg(&*get_color("#1b1cbJ")), "foo");
+  }
+
   #[test]
   #[should_panic]
   fn no_match_color() {

Also, I would add some documentation in the Readme file about this.

[TutenStain]

Thanks! I have addressed your comments and have force pushed the changes to parse and validate the colors using regexp instead.

[fcsonline]

Awesome! Merging!