Add ability to set AssemblyInformationalVersion

[hermot]

Add ability to set the AssemblyInformationalVersion attribute in an AssemblyInfo file.
This is required to be able to use nuget to build pre-release packages:

http://docs.nuget.org/docs/reference/versioning

See "Creating Prerelease Packages" point 2

[hermot]

These are the changes required to do just this:

[JeremySkinner]

Phantom isn't actually a maintained project anymore. Feel free to make the changes to the source yourself, but I'm not actually intending to make any more changes. Thanks for your interest in the project though.