GeanyVC: Add support for Fossil SCM

[nomadbyte]

I'm using Fossil SCM with most of my projects, as it's free, quite lightweight yet mighty just like Geany :). Apart from distributed Version Control, Fossil also packs Issue tracker, Wiki, Forum, and Server all in single binary executable. So pretty much all I need for my projects.

I recently found myself at an OSX machine without all of my usual toolbox ... that how I discovered Geany (BTW, excellent packaging for OSX)! But to my surprise GeanyVC did not support Fossil...

So here it is, it shouldn't be hard to add Fossil support to GeanyVC, since it mostly has similar commands and behavior as Git and Bazzar.

[nomadbyte]

Here's a test repo to try out the PR #969 :

mkdir newrepo && cd newrepo
fossil init ../newrepo.fossil
fossil open ../newrepo.fossil
echo "Test file" > testfile.txt
fossil add testfile.txt
fossil status
fossil commit -m "Added testfile"

Now in Geany, open the newrepo/testfile.txt and its revisions should be tracked by Fossil SCM, and managed using GeanyVC.