Feature documentation

[jrbeilke]

This is a big one. Everything done here is backwards compatible code-wise, and all tests are passing in Travis CI - https://travis-ci.org/jrbeilke/zabbixapi/builds/223783663

• Split up the main README and put all of the code examples into an /examples sub-directory with their own README and table of contents to better organize things.
• Added YARD and documented as much of the code as possible. Can now view the code documentation locally using "yard server" or on rubydoc.info once this PR is merged.
• Added RuboCop and updated the existing code to follow the majority of the Ruby Style guidelines.
• Tweaked the Travis CI config to speed things up with the bundler cache and fix a few build issues (mostly jruby).

[aladmit]

This is the very good job! But why did you remove test_files,executables from zabbixapi.gempsec?

[jrbeilke]

gem test was deprecated/removed so test_files is no longer needed in the gemspec - rubygems/rubygems#730

The zabbixapi gem does not include a bin/ directory, or any executables, so I removed that from the gemspec as it is an optional attribute

[aladmit]

Okay, I got it. Thank you for PR! 👍