Convert README to 1.9.3+ syntax for hash / lambdas

Converted all hashes and lambdas to Ruby 1.9.3+ Syntax. 

While it is good to allow for string keys, it may be prudent to favor symbols as their instantiation is one-half the cost (benchmark):
https://gist.github.com/baweaver/8233049

...granted the likelihood of this being a problem is minute in small projects, it can oft times be written off as nit-picky. Your mileage may vary.