Cleaning up rewrite code

[jimfleming]

Handles properties individually so we no longer need to whitelist node types.
#86 (AssignmentExpression) and #64 (rewrite cleanup)

[coveralls]

Coverage increased (+19.48%) when pulling de398a3 on jimfleming:rewrite_cleanup into adc0b95 on rdio:master.

[jimfleming]

^ Looking into test failures.

[coveralls]

Coverage increased (+19.59%) when pulling 8572c6f on jimfleming:rewrite_cleanup into adc0b95 on rdio:master.

[brettlangdon]

so much red and green, this looks awesome.

+1