Added link to ReleaseNotes.md for Choco Package

Since Chocolatey.org now supports markdown from nuspec file, adding in link to the full release notes stored in GitHub repo.  Decided not to add the full text for the release notes in the nuspec file, as this is just one more thing that needs to be remembered during the release.  Rather, point users to the one source of truth for release notes.
Merge pull request #244 from gep13/patch-2

(#240) Added link to ReleaseNotes.md for Choco Package
(#173) Fix up merge message for Stash

After actual testing on a live Stash server, it is clear that the message generated from Stash is of the format:

refs/heads/pull-requests/5/merge

and not as first thought:

refs/heads/pull-requests/5/merge-clean

Updated Acceptance Test, and also the Regex which identifies the messages, and tested on a Pull Request issued to server.  All seems to work as expected.
Merge pull request #247 from gep13/Issue173-Take2

(#173) Fix up merge message for Stash
Adding in new version of LibGit2Sharp, 0.19.0.

As a result of some changes to the core LibGit2Sharp Library, in order to properly support Stash, I am suggesting that we pull in the latest version of LibGit2Sharp.
Merge pull request #248 from gep13/LibGit2Sharp0.19.0

Adding in new version of LibGit2Sharp, 0.19.0.
Update ReleaseNotes.md

Added information about v1.2.1. release
Merge pull request #249 from gep13/patch-3

Update ReleaseNotes.md
update to newest pepita
bump test refs
fix typo
make versioning scheme configurable

-moved the scheme logic into the task since it isnt a core concern
(perhaps the exe should make use of this in the future)
simplify assembly versioing
simplify tests
split out exe test
remove redundant module init
remove redundant code
rename acceptance tests to GitVersionCore.Tests

also make testing lib consistent
rename test project
move VariableProviderTests