Add stackSafeIterationsCount param for SyncLaws, fix Sync[StateT]

[alexandru]

Issues:

• fix For the stack safety laws make the number of iterations configurable #140
• fix Add stackSafeIterationsCount param for SyncLaws, fix Sync[StateT] #138

This adds Parameters to be passed to SyncLaws, because the stack safety loops should be configurable for slower data types. For example Monix's Iterant now implements Sync, but the ScalaCheck tests for the stack safety of flatMap are timing out the Travis builds.

During this process I discovered that the Sync[StateT[F, S, ?]] is not stack safe for "repeated left binds". I fixed it by reintroducing the original AndThen in cats.effect.internals. It was originally used by Daniel in the original IO implementation.

And now Sync[StateT[F, S, ?]] is fine.

[codecov-io]

Codecov Report

Merging #138 into master will increase coverage by 0.1%.
The diff coverage is 94.11%.

@@            Coverage Diff            @@
##           master     #138     +/-   ##
=========================================
+ Coverage   89.14%   89.25%   +0.1%     
=========================================
  Files          44       46      +2     
  Lines         811      847     +36     
  Branches       59       63      +4     
=========================================
+ Hits          723      756     +33     
- Misses         88       91      +3