Merge pull request #85 from pjotrp/master

pileup in main
Merge pull request #88 from pjotrp/master

Check for samtools executable (part 1)
Merge pull request #90 from pjotrp/master

mpileup should be functional and ready for testing
merging files in complicated cases (#92)
Merge branch 'master' of github.com:lomereiter/sambamba
disable GC during header merging; #92
really disable gc during header merging; #92
fix #95
less use of GC in merge tool; closes #63; #92
depth base
per-nuc stats
depth: zero coverage option
per-sample output in depth base
depth: set default filter same as in bedtools multicov
disable GC in sort tool; default limit is 2GB now
limit memory in tests
relax min memory
basic cram support
travis builds are on mac, not ubuntu
.