Removes use of deprecated methods

This Pull Request removes (hopefully all, unless I missed any) uses of deprecated methods in the library.

##### Some key things to note:
- To make it possible for the library users to send raw data without using deprecated methods, the IrcPacket(String, IrcConnection) constructor has been made `public`.
- Deprecated methods should now be fit for removal when you see fit as there are no longer any internal calls to them.
- This branch should be merged into `master` once approved, and the `io` branch closed.