Made README.md more easily digestible.

- Simplified the markup so it didnt' render a list with improperly indented code blocks
- Updated each method definition to be an h5 element. (gives the method an anchor)
- Updated the categories to match better with how Underscore/Lodash docs define/categorize their methods
updated README
updating folder structure
updating arrays::flatten to be in parity with underscore
fixing small errors
fixing untracked files
updating tests
tests passing
tests passing
Merge pull request #8 from bmcminn/master

Aligned project with Underscore/Lodash by @bmcminn