Normalize NSEDoc documentation of scripts.

I made every script follow a standard form: it starts with the id, followed by
the description. The description is contained in [[ ]] delimiters. The
description is in the global description variable, not in a LuaDoc comment.
Other LuaDoc information such as @args and @usage follows the description in a
comment.

The first paragraph of each description is a a short summary of what the script
does. More detailed information, if any, is given in following paragraphs.

I also improved some wording and formatting in a few cases.

scripts/HTTPtrace.nse

@@ -1,6 +1,11 @@
---- Sends and HTTP TRACE and describes any modifications
---
---@output
+id = "HTTP TRACE"
+description = [[
+Sends an HTTP TRACE request and shows header fields that were modified in the
+response.
+]]
+
+---
+-- @output
 -- 80/tcp open  http \n
 -- |  HTTP TRACE: Response differs from request.  First 5 additional lines: \n
 -- |  Cookie: UID=d4287aa38d02f409841b4e0c0050c13148a85d01c0c0a154d4ef56dfc2b4fc1b0 \n
@@ -11,10 +16,6 @@
 
 -- 08/31/2007
 
-id = "HTTP TRACE"
-
-description = "Send HTTP TRACE method and print modifications"
-
 author = "Kris Katterjohn <katterjohn@gmail.com>"
 
 license = "Same as Nmap--See http://nmap.org/book/man-legal.html"