signed Google.Maps with a strong name key
made GoogleSigned.GetSignature thread safe

A hash algorythm is not threadsafe, thus GetSignature was not thread
safe when a single instance of the hash algorythm was shared all
concurent calls.
cleaned up no longer used code
Merge pull request #8 from IsNull/master

- Assembly signed with strong name key
- made GoogleSigned.GetSignature thread safe.