Adding last line class with one-liner check

[prpetten]

This commit fixes #66

• Wrote failing test under describe 'analyzing 1 line methods' do ... block
• Fixed one line method definition counts, by fixing the underlying issue in the SandiMeter::Analyzer#last_line method.
• Refactored internals of SandiMeter::Analyzer#last_line into its own class with corresponding specs and documentation.
• Added attr_reader for file_lines instance variable
• Added .idea/ to .gitignore for Rubymine usage during development
• Added 2.2, 2.3, and gem install bundler -v 1.13.1 to .travis.yml for completeness and to fix issue with TravisCI and jruby-head not having bundler installed
• Added minor version dependency to json gem at ~> 1.8.3 as 2.0.0 and higher require ruby to be at 2.0 or higher, which was causing build at 1.9.3 to fail.

[prpetten]

Not sure why TravisCI didn't update status, but here is the latest build.

[roooodcastro]

I'm having the same issue, and this PR seems to fix it. @makaroni4 please review this

[roooodcastro]

I created a fork for me of your branch, but I noticed that there's still an issue:

At line 26 of the last_line.rb file, the method determine_last_line returns nil if the method is a oneliner. This causes sandi_meter to think that the method is misindented because it has no end, and thus cause the method to be counted as an invalid method. This caused my rule 2 percentage to be much lower than it should (no difference between original and your fork).

The fix was making determine_last_line return start_line_number if the method is a oneliner.