Documentation formatting and cleanup

Following what appears to be the predominant style, format
names of commands and commandlines both as `teletype text`.

While we're at it, add articles ("a" and "the") in some
places, italicize the name of the command in the manual page
synopsis line, and add a comma or two where it seems appropriate.

Signed-off-by: Jonathan Nieder <jrnieder@uchicago.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/git.txt b/Documentation/git.txt
index 1978e1b..bb33c40 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -483,10 +483,10 @@
 	a pager.
 
 'GIT_SSH'::
-	If this environment variable is set then linkgit:git-fetch[1]
-	and linkgit:git-push[1] will use this command instead
+	If this environment variable is set then `git-fetch`
+	and `git-push` will use this command instead
 	of `ssh` when they need to connect to a remote system.
-	The 'GIT_SSH' command will be given exactly two arguments:
+	The '$GIT_SSH' command will be given exactly two arguments:
 	the 'username@host' (or just 'host') from the URL and the
 	shell command to execute on that remote system.
 +
@@ -500,8 +500,8 @@
 
 'GIT_FLUSH'::
 	If this environment variable is set to "1", then commands such
-	as git-blame (in incremental mode), git-rev-list, git-log,
-	git-whatchanged, etc., will force a flush of the output stream
+	as `git-blame` (in incremental mode), `git-rev-list`, `git-log`,
+	and `git-whatchanged` will force a flush of the output stream
 	after each commit-oriented record have been flushed.   If this
 	variable is set to "0", the output of these commands will be done
 	using completely buffered I/O.   If this environment variable is