Made Piston compile without PortAudio settings

Closes https://github.com/PistonDevelopers/piston/issues/371
Merge pull request #373 from bvssvni/master

Made Piston compile without PortAudio settings
Removed debug comments

Closes https://github.com/PistonDevelopers/piston/issues/374
Merge pull request #375 from bvssvni/master

Removed debug comments
Added example to `GameIterator` docs

Closes https://github.com/PistonDevelopers/piston/issues/376
Merge pull request #377 from bvssvni/master

Added example to `GameIterator` docs
Added creation of graphics context to `GameIterator` docs

Closes https://github.com/PistonDevelopers/piston/issues/378
Merge pull request #379 from bvssvni/master

Added creation of graphics context to `GameIterator` docs
Updated `GameIterator` docs with 'ref' and 'mut'

Closes https://github.com/PistonDevelopers/piston/issues/380
Merge pull request #381 from bvssvni/master

Updated `GameIterator` docs with 'ref' and 'mut'
Removed constructor from `GameWindow` trait

Closes https://github.com/PistonDevelopers/piston/issues/383
Merge pull request #385 from bvssvni/master

Removed constructor from `GameWindow` trait