rake-compiler and bundler integration fixes
Update hash key descriptions in README for SerialPort.new

The code at https://github.com/hparra/ruby-serialport/blob/master/ext/native/serialport.c#L422 looks like it uses the hash keys "baud", "data_bits", and "stop_bits", rather than "baudrate", "databits", and "stopbits".
Support for Travis CI
v1.2.0 release