(nit) use native travis rust support

This should speed up build times
(feat) build status in bare bones README.md
(cleanup) Rename crate to content_type.

Snake case crate and package names are preferred over squashed case ones.

Crate naming conventions: https://aturon.github.io/style/naming.html
Implied package naming conventions: https://crates.io
Merge pull request #1 from michaelsproul/cleanup/crate-rename

(cleanup) Rename crate and package to content_type.
Merge pull request #2 from brycefisher/feat/build-status

Feat/build status
temp fix.