parse UUID

Nice & easy tool for converting string to UUID:

# login to ruby shell
yasemin$ irb

# Make sure UUID tools is loaded. 
>> UUIDTools
NameError: uninitialized constant UUIDTools
 from (irb):1
>> require "uuidtools"
=> true
>> UUIDTools
=> UUIDTools

# Parse string to UUID
>> UUIDTools::UUID.parse_hexdigest(s).to_s
>> UUIDTools::UUID.parse_hexdigest("CEBBA579AE1A4C4A9EE0D1BCDC8C3E1E").to_s
=> "cebba579-ae1a-4c4a-9ee0-d1bcdc8c3e1e"