Remerge some files in order to reduce number of additional files

Make necessary changes for split, rename files, reorganize some bits

Add python script to doc/protocol.txt

finite liquid

- Neatly placed all emerge related code into a new file, emerge.cpp
- Greatly cleaned up the code in EmergeThread::Thread()
- Reworked Emerge queue.  Now an actual std::queue of v3s16 block positions
- Removed the completely unnecessary map of peer ids requesting blocks