First version of `js2r-kill`

Expect edge-cases
Adds support for killing with parse errors

When the buffer has parse errors, fallback to `kill-line`
More robust killing support within functions
Adds more tests for js2r-kill
Adds some comments for `js2r-kill` and related functions
Better function naming
Check for js2 parse errors only in `js2r--kill-line-in-balanced-exp`
Cleanup

- removes some leftovers
- fixes a typo
Merge pull request #25 from NicolasPetton/js2r-paredit-kill

Implements `js2r-kill`
Add @NicolasPetton to list of contributors
Update README.md