added script to start testing environment
added ErrMissing Backend

Changes functionality. For the gobfilebackend, this error will be raised
if the file can't be found. Be sure to create it!
Mostly formatting
Added error return on NewSqlAuthBackend
Made Users() return an error

Added tests to make sure backends are valid for an authorizer.
made mongodb backend return error on creation
Updated example server
updated readme and server example