Added 'slow' tag to async tests.

The timeout tests would take 10 seconds to run. Not good for rapid feedback
Added CommandLineParser package
Removed unused project refs from self tests
Added ref from specs to runner
Remove nuget restore target

Replaced by paket restore
Removed nuget.exe
Updated guardfiles

Don't create assembly info files when quick-testing with guard. Creating
new assembly info files just causes the build to run again, which creates
new assembly info files, etc.
Introduced CommandLineParser

This should allow us to specify arguments for the runner
Optimized guard

Only build what is necessary to run tests after a file change