Merge pull request #254 from scidom/master

Added basic functionality for complex numbers
Small fixes in Time. Added TimeSpan#from_now, TimeSpan#ago, MonthSpan#from_now and MonthSpan#ago
Added spec for Complex#to_s when imag is negative
Added missing Char#<=>
Removed all `#!/usr/bin/env`
Added a `pretty_json` utility to samples