Ignore iml files
Add writeSerialHex method

* Added a new method to support sending hex strings from js like e.g. "ffaa55"
which will get converted to byte arrays where two hex chars get packed into one byte.
I.e. the method will turn "ffaa55" into a byte array of 3 bytes; java would naturally
create a 6 byte long array from the given string.
* Didn't touch writeSerial to not break any existing code built on this when updating the lib
* Added a helper method for creating the proper byte array from a given hex string
* Updated serial.js to expose the new method