Documentation: don't link to example mail addresses

Email addresses in documentation are converted into mailto: hyperlinks
in the HTML output and footnotes in man pages.  This isn't desirable for
cases where the address is used as an example and is not valid.

Particularly annoying is the example "jane@laptop.(none)" which appears
in git-shortlog(1) as "jane@laptop[1].(none)", with note 1 saying:

	1. jane@laptop
	   mailto:jane@laptop

Fix this by escaping these email addresses with a leading backslash, to
prevent Asciidoc expanding them as inline macros.

In the case of mailmap.txt, render the address monospaced so that it
matches the block examples surrounding that paragraph.
Helped-by: NJeff King <peff@peff.net>
Signed-off-by: NJohn Keeping <john@keeping.me.uk>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-fast-import.txt

@@ -427,7 +427,7 @@ they made it.
 
 Here `<name>` is the person's display name (for example
 ``Com M Itter'') and `<email>` is the person's email address
-(``cm@example.com'').  `LT` and `GT` are the literal less-than (\x3c)
+(``\cm@example.com'').  `LT` and `GT` are the literal less-than (\x3c)
 and greater-than (\x3e) symbols.  These are required to delimit
 the email address from the other fields in the line.  Note that
 `<name>` and `<email>` are free-form and may contain any sequence

Documentation/git-tag.txt

@@ -129,7 +129,7 @@ This option is only applicable when listing tags without annotation lines.
 CONFIGURATION
 -------------
 By default, 'git tag' in sign-with-default mode (-s) will use your
-committer identity (of the form "Your Name <your@email.address>") to
+committer identity (of the form "Your Name <\your@email.address>") to
 find a key.  If you want to use a different default key, you can specify
 it in the repository configuration as follows:
 

Documentation/mailmap.txt

@@ -46,7 +46,7 @@ Jane Doe         <jane@desktop.(none)>
 Joe R. Developer <joe@example.com>
 ------------
 
-Note how there is no need for an entry for <jane@laptop.(none)>, because the
+Note how there is no need for an entry for `<jane@laptop.(none)>`, because the
 real name of that author is already correct.
 
 Example 2: Your repository contains commits from the following