Add ref alignments histogram

histogram of the count of alignments per reference name
refactor a bit
Factored out the BAMTOOLS variable into the shell
now instead of defining BAMTOOLS in Makefile, it is taken from the shell
To build, use the form of `BAMTOOLS=<path-to-bamtools> make'
Merge branch 'master' of https://github.com/chmille4/bamstatsAlive
Using the library 'jansson-2.5' to handle json