Check md5 sums of downloaded files against expectation

[envest]

Sometimes things go wrong quietly while downloading files. We know what the md5 sums should be, so we can check them.

[envest]

Something like

# md5sum --check checks.tsv
data/BRCAarray.pcl: OK
data/BRCAClin.tsv: OK
data/BRCARNASeq.pcl: OK
data/BRCARNASeqClin.tsv: OK

where checks.tsv is formatted like

1a89ea769381e300e5a88ec61713ad9e	data/BRCAarray.pcl
8c76a476c5b6f4f8deec017c876db156	data/BRCAClin.tsv
7f00ea6ef1f309773b02e6118046550f	data/BRCARNASeq.pcl
d4486dde14da14b4f8887a7415e2866f	data/BRCARNASeqClin.tsv