Merge pull request #42 from csherratt/swap_buffers

swap buffer only on CastSwapBuffers
ignoring .dir-locals.el
Merge pull request #44 from photex/master

ignoring .dir-locals.el
Merge pull request #45 from csherratt/index_slice

expose IndexSlice
Merge branch 'envir' of https://github.com/kvark/gfx-rs into kvark-envir

Conflicts:
	src/gfx/lib.rs
Merge branch 'kvark-envir'
-Add nicer error prints when the Enviroment errors out.
-Fix a typo ValueI32Vec instead of ValueF32Vec