Emp updates

[wasade]

Depends on #29. This is WIP, please do not merge yet.

[wasade]

Taxon searching:

# get all features descending from a taxon
$ redbiom search taxon --context test o__Xanthomonadales
TACGAAGGGTGCAAGCGTTACTCGGAATTACTGGGCGTAAAGCGTGCGTAGGTGGTCGTTTAAGTCCGTTGTGAAAGCCCTGGGCTCAACCTGGGAACTG
TACGAAGGGTGCAAGCGTTACTCGGAATTACTGGGCGTAAAGCGTGCGTAGGTGGTTTGTTAAGTCTGATGTGAAAGCCCTGGGCTCAACCTGGGAATTG
TACGAAGGGTGCAAGCGTTACTCGGAATTACTGGGCGTAAAGCGTGCGTAGGTGGTTATTTAAGTCCGTTGTGAAAGCCCTGGGCTCAACCTGGGAACTG

# search for samples containing those features
$ redbiom search taxon --context test o__Xanthomonadales | redbiom search observations --context test
UNTAGGED_10317.000003302
UNTAGGED_10317.000001405

# do other fun things like summarize the samples
$ redbiom search taxon --context test o__Xanthomonadales | redbiom search observations --context test | redbiom summarize samples --category SAMPLE_TYPE
Stool   1
Forehead    1

Total samples   2

Extract feature IDs from samples:

# get the features associated with a set of samples
$ redbiom select observations-from-samples --context test 10317.000047188 10317.000005080 | wc -l
     492

# get only the features common between a set of samples
$ redbiom select observations-from-samples --exact --context test 10317.000047188 10317.000005080 | wc -l
      85

# do other fun things like find other samples containing those features
$ redbiom select observations-from-samples --exact --context test 10317.000047188 10317.000005080 | redbiom search observations --context test | wc -l
      12

[wasade]

Two missing components: fetching or summarizing taxonomy information.