Use MobaDiff with git difftool

Recently there's an activity in IT that forces the deletion of all
unauthorized softwares from all work machines.

Unfortunately, kdiff3 is one in the list.

As it is generally okay to use vimdiff as an alternative for kdiff3, A
gui tool is better suited for desktop workflows.

Known that MobaXterm is shipping a gui diff tool named MobaDiff. But
it only appears in the windows right click context menu.

Find the real application name takes me some time to search in the
windows registry. "MobaRTE.exe", which is the one invoked by
HKCR\*\shell\MobaDiff. And it was invoked with "-contextdiff" switch
to show MobaDiff UI, while when the switch is "-contextedit" it shows
MobaTextEditor.

Too bad that the "-contextdiff" switch do not support pre-image
post-image as other diff tool did, which effectively made it unable to
be used as a command line diff utility.

Also MobaTech did not mention anything in their document of this
MobaRTE application.

Finding the correct parameter and switches to invoke it as an ordinary
diff utility takes me lots of time. In the MobaXterm document, it was
said "MobaXterm.exe" will accept the "-compfiles" parameter which will
invoke the MobaDiff interface. But it does not work in my system,
actually MobaXterm.exe when invoked with -compfiles parameter will
hang there showing a splash banner only. I have to use Ctrl-C in the
terminal to stop it.

The good thing is, "MobaRTE" accepts the "-compfiles" switch also, and
it accepts those pre-image and post-image filenames parameters.

Now it works like a diff utility. And here's my setup:

```
git config --global diff.guitool moba
git config --global difftool.moba.cmd '"C:\Program Files
(x86)\Mobatek\MobaXterm\MobaRTE" -compfiles $LOCAL $REMOTE'
```