Add standard .gitignores

MSP-9818
Semantic Versioning 2.0.0

MSP-9818
Add travis-ci support

MSP-9818

Configuration in .travis.yml and build status badge in README.
simplecov

MSP-9818
CodeClimate badge

MSP-9818
Coveralls

MSP-9818

Add support for coveralls.io upload to spec_helper.rb and add badge to
README.
Rubygems badge

MSP-9818
Fix gemspec warnings

MSP-9818

Fill in description and summary.  Add `~>` versions to eliminate
semantic versioning warnings.
Add correct BSD 3-clause license

MSP-9818

Metasploit projects use the BSD 3-clause instead of the default MIT
license.
YARD

MSP-9818

Add yard to documentat yard-metasploit-erd itself.  Add the code to make
this gem a yard plugin won't occur as part of the skeleton build out.
Ignore .rvmrvc; fix README link
Merge pull request #1 from rapid7/feature/gem-skeleton

Gem skeleton