Merge pull request #456 from bvssvni/master

Removed `to_sendable`
Merge pull request #457 from bvssvni/master

Implemented `Iterator` for `GameIterator`
Added maintainers

Closes https://github.com/PistonDevelopers/piston/issues/306
Initial concurrency, lots of code duplication though
pre-merge working state
manual merge
working concurrency
fix pub use statements
remove [feature(globs)]
Added notice about outdated information
Exit nicely
Added instructions for how to build Piston

Closes https://github.com/PistonDevelopers/piston/issues/461
Move windows into tuple
Merge pull request #458 from gmorenz/concurrency-up-to-date

Introduce `ConcurrentGame`