replace doParallelWithThrottle with LINQ's AsParallel

delete AsyncHelper module
Merge pull request #193 from vasily-kirichenko/develop

Replace doParallelWithThrottle with LINQ's AsParallel
Fixes #191
API docs git helpers
Merge pull request #194 from ovatsus/develop

Fixes #191
Merge branch 'develop' of github.com:fsharp/FAKE into develop
API docs git helpers