zsh-completion: fix issue with [.md, add basic -L completion, remove extra _files args (#168)

- Use array `commands=(...)` and `_describe` to deal with '[.md' & empty cache scenario.  Fixes #166
- Hide `tldr --list` stderr (`2>/dev/null`) which breaks completion with empty cache
- Remove `sed` since #112 changed commas to newlines
- Add new `sed`-equivalent replacement (`:` -> `\:`) using native [ZSH `${name//pattern/repl}`](http://zsh.sourceforge.net/Doc/Release/Expansion.html#Parameter-Expansion) since colon is special character in ZSH completions
- Add basic support for `-L, --language` flag from #125. In future, can consider adding extra completions maybe based on caches `pages.{lang}` folders.
- Remove extraneous completion of file names for positional arguments (i.e. `'*:file:_files'`)

zsh_tealdeer

@@ -1,7 +1,9 @@
 #compdef tldr
 
 _applications() {
-  _values 'applications' "${(uonzf)$(tldr --list | sed -e 's/, /\n/g')}"
+    local -a commands
+    commands=(${(uonzf)"$(tldr --list 2>/dev/null)"//:/\\:})
+    _describe -t commands 'command' commands
 }
 
 _tealdeer() {
@@ -18,6 +20,7 @@ _tealdeer() {
             sunos
             windows
         ))'
+        "($I -L --language)"{-L,--language}"[Override the language settings]:lang"
         "($I -u --update)"{-u,--update}"[Update the local cache]"
         "($I -c --clear-cache)"{-c,--clear-cache}"[Clear the local cache]"
         "($I -p --pager)"{-p,--pager}"[Use a pager to page output]"
@@ -31,8 +34,7 @@ _tealdeer() {
             never
         ))"
         '(- *)'{-h,--help}'[Display help]'
-            '(- *)'{-v,--version}'[Show version information]'
-            '*:file:_files'
+        '(- *)'{-v,--version}'[Show version information]'
         '1: :_applications'
     )