Replace code generator with python script

- New bindings generator written in Python using Jinja2 lives in
  bindings/
- Added new NeovimConnector::send for QList<QByteArray>
- Moved msgpack decoding methods from NeovimConnector, they are now
  functions in the NeovimQt:: namespace - all share a similar signature
  bool decodeMsgpack(msgpack_object, targettype&)
- Removed the old code generator. Generating C++ from C++ was getting
  a bit convoluted
- NeovimConnector::decode will now fallback to utf8 if the decoding is
  not available
- NeovimRequest now takes NeovimConnector as argument, this is required
  to decode error strings
- Fixed tst_neovimobject, the send_event() is now called rpcnotify()
- Updated README file