Parse response ignoring echo and init messages

I've modified the parsing of responses to ignore any echo or init message that appear before the actual response. Tests where updated to mock the actual responses from a ELM327 device using carriage returns (char 13). This makes possible to use the commands with or without echo enabled and to ignore bus startup messages that might otherwise cause errors.

This is related to: https://github.com/pires/android-obd-reader/issues/16