Trimmed mean coverage

As well as getting trimmed mean coverage to be included, also changed a few other things so development was simplified (no more messing with pythonpath, and can run this as a dev/testing cmdline). Maybe I was just doing it wrong....
```
BamM/c$ make && ../bin/bamm parse --coverages /dev/stdout -m tpmean ~/git/BamM/test/data/1_shaddow.bam
```
Also had issues with incorrect path being specified to the libBamM.a file, but you must have already solved this? Maybe I just broke it (see change in ` bamm/cWrapper.py`)