Squashed 'vendor/samtools/' content from commit 5f2c744

git-subtree-dir: vendor/samtools
git-subtree-split: 5f2c744c22c5c2d313ad73c594bdca244aa2dfa9
Merge commit '71efc3091b4c80f54a8ae06d4bb80510ab451c7b' as 'vendor/samtools'
add samtools as a subtree, build it and gtest directly

instead of using externalproject_add
bundle the required bits of boost