Merge pull request #50 from csherratt/master

updated to work with new closure types
Add Colin Sherratt to AUTHORS
Represent most nullable ptrs as `Option<*T>`s in the ffi
Merge pull request #51 from bjz/nullable-ptrs

Represent most nullable ptrs as `Option<*T>`s in the ffi
Revert "Merge pull request #51 from bjz/nullable-ptrs"

This reverts commit eb56cc4249fa3aa18ed22082350d513e726fa4a0, reversing
changes made to a440aad5071340951ff4421e89ef6f46f35802cf.
Added examples to travis
Added #[feature(link_args)]; to allow fix build.