Extended the CBOR decoder & encoder:

- added support for reading various sized integers;
- added support for reading tags;
- simplified the encoder to no longer need introspection for writing
  certain types, but leave that up to the caller of the encoder.
Checked off a to do.
Renamed CborOutputStream to CborEncoder:

- better suits its purpose;
- renamed all tests accordingly.
Simplified the decoder API:

- simplified the decoder API by removing redundant methods;
- simplified the implementation of the decoder methods a bit;
- renamed the CborInputStream to CborDecoder to better reflect its purpose;
- renamed all tests accordingly.
Small cleanups & bug fixes.