ensure a consistent style for all changes

[softprops]

Issue #, if available:

Description of changes:

I found in another pull that I wasn't able to fmt sources without incurring a bigger git diff of unrelated files. Formatting files is actually good for contributors because its often a feature of rust's efforts to improve the quality of life tools like rls and its vscode extension ( which auto formats on save ). Consistency is also good for readability.

Included is

• an updated travis config adds a nightly check ( the rustfmt config this project uses requires nightly ) for rustfmt
• an update to contributing file to give contributors a heads up
• some helpful links for those new to the project ( and rustfmt ) what these style configs rules do

By submitting this pull request

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I confirm that I've made a best effort attempt to update all relevant documentation.

[softprops]

going to wait on travis before actually applying the style rules to see what happens in the case the style rules aren't honored

[softprops]

check seemed to fail without fmting so that worked

[softprops]

noting here that the ALLOW_FAILURES=true env var probably doesn't do what you think it does

[davidbarsky]

noting here that the ALLOW_FAILURES=true env var probably doesn't do what you think it does

Damn, okay. I'll need to learn how Travis works one of these days.

I found in another pull that I wasn't able to fmt sources without incurring a bigger git diff of unrelated files. Formatting files is actually good for contributors because its often a feature of rust's efforts to improve the quality of life tools like rls and its vscode extension ( which auto formats on save ). Consistency is also good for readability.

Totally agree. I was using rustfmt 1.0, but Travis, for whatever reason, had 0.99, which had a slightly different formatting config, which would cause failures.

Thanks for setting this up!