Added the qextserial-library, which lets QT communicate with serial
ports.

Adapted the functions:
- Threw out the debugger hints
- "write" in HFSSerial now replaces "writeChar" and "writeChars" with
overloading - is easier to call.
- Added some explaining comments

After Downloading, the qextserial-lib can be ignored by git with
gitignore, because there won't be a change on the libs in the future.