Upgrade to Rust Edition 2018

[jan-auer]

This PR is a first pass over the code base in an attempt to modernize it. Changes include:

• Breaking: Updated to Rust Edition 2018
• Breaking: Upgraded uuid dependency
• Renamed a bunch of internal methods (e.g. new -> parse) or replaced functions with methods (e.g. parse_header -> DBIHeader::parse)
• Ensure that no internal types are accidentally exposed by using pub(crate)

Also, two more Travis jobs have been added to check rustfmt and clippy with preset clippy::all. This should make changes to the crate more consistent going forward.

This is by far not complete, but it should make working with the crate and modern tooling far easier. I've deliberately not added anything like precommit hooks, since these are usually a pain to maintain down the road.

More tempting things to do would be to add #![warn(missing_docs] to the root module and separately to replace FallibleIterator, but that is for a later PR :)

[rlabrecque]

Nice! I hit this when first trying this out. I had <2 days worth of Rust experience and was trying to get it working on Rust2018, wasn't super fun.

[willglynn]

This looks great! I especially like how you broke the work into reviewable, focused commits. I request no changes 😄 I'm also in awe of all the syntax that didn't exist two years ago, like shorthand struct literals (1.17) or pub(crate) (1.18).

Expect a 0.3.0 release containing this PR shortly. Thanks again!

[jan-auer]

Thanks for the quick response! No rush for a release on my end :)