Syntax documentation rewrite for C-commands

Rewrote the syntax documentation for all the commands starting with the
letter C.

docs/help/in/completion.in

@@ -1,31 +1,31 @@
 
+Syntax:
+
 @SYNTAX:completion@
 
-Irssi can "complete" some words for you - you can write just first few letters
-of the word and press TAB (or any other key with action word_completion
-assigned). Then, irssi will choose the most probable matching word and inserts
-it to the command line. You can press TAB repetitively and irssi will replace
-the chosen word with another possible words matching to the letters you wrote.
+Parameters:
 
-The words chosen usually depend on their context - they can be filenames or
-command names, but most frequently they are nicks of people on same channels as
-you are. However, you can have global list of own completions, which apply to
-all contexts. This command is dedicated to maintaining of such a list.
+    -auto:      Insert the completion without pressing a word completion character.
+    -delete:    Removes the completion from the list.
+    
+    A key and the value to use as a replacement. If no argument is given, the
+    list of completions will be displayed.
 
-Without any parameters, /COMPLETION displays list of all user completions.
+Description:
 
-/COMPLETION [-auto] <prefix> <string> adds completion which gets triggered when
-you press TAB (or any other key with action word_completion assigned) after
-writing <prefix> specified and which expands to <string>. When -auto is
-specified, the completion gets triggered even when you press SPACE or ENTER (or
-any other key with action check_replaces assigned) after the <prefix>. If
-there's already some <prefix> completion in the list, it will get replaced.
+    Replaces or completed words or letters; you can write just the first few
+    letters of the word and press TAB to insert a replacement.
 
-/COMPLETION -delete <prefix> removes completion of <prefix> from the user
-completion list.
+    When a replacement has been found, Irssi will choose the most probable
+    matching word and replaces it; you may press TAB repeatedly to swap between
+    matches.
 
-Note: When -auto is specified for the <prefix> you want to remove you have to 
-quote it like /COMPLETION -delete '<prefix>'. Works with doublequotes aswell.
+Examples:
+
+    /COMPLETION w/h without
+    /COMPLETION -auto compr compromised
+    /COMPLETION -delete 'compr'
+    /COMPLETION -delete without
 
 See also: BIND