colorize: add README and refactor plugin (#7314)

plugins/colorize/README.md

+# colorize
+
+With this plugin you can syntax-highlight file contents of over 300 supported languages and other text formats.
+
+To use it, add colorize to the plugins array of your zshrc file:
+```
+plugins=(... colorize)
+```
+
+## Usage
+
+* `ccat <file> [files]`: colorize the contents of the file (or files, if more than one are provided). If no arguments are passed it will colorize the standard input or stdin.
+
+Colorize will highlight the content based on the filename extension. If it can't find a syntax-highlighting method for a given extension, it will try to find one by looking at the file contents. If no highlight method is found it will just cat the file normally, without syntax highlighting.
+
+## Requirements
+
+You have to install Pygments first: [pygments.org](http://pygments.org/download/)

plugins/colorize/colorize.plugin.zsh

-# Plugin for highlighting file content
-# Plugin highlights file content based on the filename extension.
-# If no highlighting method supported for given extension then it tries 
-# guess it by looking for file content.
-
-#easier alias to use plugin
+# easier alias to use the plugin
 alias ccat='colorize_via_pygmentize'
 
 colorize_via_pygmentize() {
@@ -12,16 +7,20 @@ colorize_via_pygmentize() {
         return 1
     fi
 
+    # pygmentize stdin if no arguments passed
     if [ $# -eq 0 ]; then
-        pygmentize -g $@
+        pygmentize -g
+        return $?
     fi
 
+    # guess lexer from file extension, or
+    # guess it from file contents if unsuccessful
+    local FNAME lexer
     for FNAME in $@
     do
-        filename=$(basename "$FNAME")
-        lexer=`pygmentize -N \"$filename\"`
-        if [ "Z$lexer" != "Ztext" ]; then
-            pygmentize -l $lexer "$FNAME"
+        lexer=$(pygmentize -N "$FNAME")
+        if [[ $lexer != text ]]; then
+            pygmentize -l "$lexer" "$FNAME"
         else
             pygmentize -g "$FNAME"
         fi