Fix Scala Form documentation

Parameters for the `mapping` method are wrong in some examples: (A.apply)(A.unapply), instead of (A.apply, A.unapply)
Fixed small indentation in SBTSubProjects.md
Merge pull request #858 from studiodev/patch-2

Fix Scala Form documentation
Merge pull request #866 from wm3/master

Fixed indentation in SBTSubProjects.md