Release version 0.4.0-alpha.1

[abelbraaksma]

Releasing an alpha version as some of the features I want completed in 0.4.0 are not completed yet. These are the relevant release notes:

0.4.0-alpha.1

Some highlights, but see Release 0.4.0.-alpha.1 for details

• fixes not calling Dispose for 'use!', 'use', or finally blocks #157 (by @bartelink)
• BREAKING CHANGE: null args now raise ArgumentNullException instead of NullReferenceException, #127
• adds TaskSeq.takeWhile, takeWhileAsync, takeWhileInclusive, takeWhileInclusiveAsync, #126 (by @bartelink)
• adds AsyncSeq vs TaskSeq comparison chart, #131
• removes release-notes.txt from file dependencies, but keep in the package, #138