Updated fossil to version 1.27, modified package structure to comply wit...

Hi, here's my update for the fossil package:

I've moved the package logic in package fossil.portable to follow [package portable guidelines] (https://github.com/chocolatey/chocolatey/wiki/ChocolateyFAQs#what-is-the-difference-between-packages-named-install-ie-gitinstall-portable-ie-gitportable-and--ie-git) and therefore created a fossil.portable package containing the install script and modified the main fossil package to just have a dependency to fossil.portable in the nuspec file.

Then i've updated version to current one (1.27) and added fossil [changelist](http://www.fossil-scm.org/download.html) in releasenotes nuspec element.

I've also added an empty uninstall script to avoid warning about lack of it during uninstall process.

Check if everything is fine and make me know,
Thank you