Merge pull request #34 from dannycoates/srp1

copied Jed's srp.js to lib
add SRP configuration params
Merge pull request #37 from mozilla/srp_config

add SRP configuration params
appease the jshint gods
implement utilities to compute hmac/xor keys and encrypt response for getSignToken2
Merge pull request #42 from mozilla/srp_utils

implement utilities to compute hmac/xor keys and encrypt response for ge...
Began implementing SRP