Add VersionPrefix support to csproj, vbproj, fsproj, and props files

[Invvard]

In *.csproj and *.props files, by default, Version is composed of VersionPrefix and VersionSuffix, and only VersionPrefix, if VersionSuffix is blank.

Andrew Lock explain this very well in this blog post : Version vs VersionSuffix vs PackageVersion: What do they all mean?

I only added support for VersionPrefix for those file type because I know they exist and are used, not so sure for other supported files.

Tests for those 2 file types are updated.

I did not find any contribution directives, so I went for the obvious edits but if something is missing, I'll be happy to comply :)

[vers-one]

Thank you for your contribution!

The change looks great. One more thing I would add to this pull request before merging it is an update to the README.md file. There is Additional notes section that lists all the supported tags. Since we're adding one more tag, we need to mention it there as well.

[Invvard]

Hi,
Always a pleasure to contribute!

I added the VersionPrefix to fsproj and vbproj as well.
Additional notes have been updated and I took the liberty to split nuspec files from other types as it only look for the Version tag. I hope I did not overstep but if you prefer I rollback this change just say the word :)

[vers-one]

Thank you!

Released in version 1.5.