Encoding value change

OK, so setting the data_coding value on a smpp.PDU object results in an exception. There does not seem to be a way to encode a message when this is set to 0. It should encode it using ASCII. I modified the defs.js file to change the value of ASCII to 0, since apparently this is an expected behavior when the message is not in UCS2.

v0.3.3

Update README.md

v0.3.2: Manually merge pull request for PDU encoding

• Adding in PDU encoding bugfix from original project pull request