NB: This requires hivex >= 1.3.2 before this syntax becomes true.

Turn:

 =item B<-a> | B<--all>

into:

 =item B<-a>

 =item B<--all>

This gives a more natural-looking manual page, as well as making it
easier to directly link to these sections.

This adds support for various Registry keys under HKEY_USERS (user
preferences).

(1) HKEY_USERS\<SID>
    where <SID> is a User SID.

For example:

  # virt-win-reg Windows 'HKEY_USERS\S-1-5-19'

lists out the LocalService user's registry.

(2) HKEY_USERS\<username>
    where <username> is a Windows local username (this is a
    libguestfs extension).

For example:

  # virt-win-reg Windows 'HKEY_USERS\rjones'

lists out the user preferences of user 'rjones'.

HKU can be used as an abbreviation for HKEY_USERS.  Merging is also
supported.

The crucial change is the tuple that is returned by map_path_to_hive:

-    my ($hivename, [...]) = map_path_to_hive ($_);
+    my ($hiveshortname, $hivefile, [...]) = map_path_to_hive ($_);

Previously the $hivename was both the name of the hive (eg. "sam"),
the name of the local copy in /tmp, and the name of the hive in
%systemroot%\system32\config.

In the new code, the $hiveshortname (eg. "sam") is still used for the
local copy in /tmp, but we return $hivefile which is the full Windows
path (eg. "/windows/system32/config/sam").

The purpose of this change is to allow us in future to return hives
from other Windows directories, specifically HKEY_USERS hives from
Windows home directories.

Although this is just code motion, it requires some quite extensive
changes to virt-win-reg.

This also requires hivex >= 1.2.7.

This is now used consistently across all the documentation.