Fix errors/typos/nits on the nightly task

* Document the very cool nightly task
* Fix a couple issues with the nightly task
* Add nightly files to the .gitignore
Basic travis configuration
Merge pull request #9 from tomjakubowski/nightly-fixes

Fix errors/typos/nits on the nightly task
Merge pull request #10 from tomjakubowski/travis

basic Travis-CI configuration
Fix bug breaking enum indexing
Merge pull request #11 from wycats/master

Fix Enum indexing
Add support for primitive types

Rustdoc recently added pages + indexes for the primitive types here:
mozilla/rust@c2e3aa37daedf698072b4aadbc420f24505b2b2d

Also roll DocsetIndex::ITEM_TYPE into an array.