Add batching to dossier.store.
Reduce the number of 'put' calls for indexes.

For *each* call to `store.put` (given K feature collections), there
is now a single `kvl.put` for storing the FCs and `N` `kvl.put`s
where `N` is the number of indexes defined.

In other words, the number of puts is not tied to the number of FCs.
made a simple script for comparing compression performance on
FeatureCollections, which is relevant to dossier.store, because it
could/should transparently compress things; or maybe kvlayer
could/should.
adding better doc string with example output:

raw:    423 MB of FC data, 1.000 compression, 0.000 seconds --> inf MB/sec compression, 0.000 seconds --> 0.000 MB/sec decompression
xz:     34 MB of FC data, 0.081 compression, 164.662 seconds --> 0.208 MB/sec compression, 3.169 seconds --> 10.786 MB/sec decompression
gz:     75 MB of FC data, 0.178 compression, 17.321 seconds --> 4.358 MB/sec compression, 2.584 seconds --> 29.220 MB/sec decompression
bz2:    38 MB of FC data, 0.090 compression, 44.640 seconds --> 0.857 MB/sec compression, 10.356 seconds --> 3.696 MB/sec decompression
snappy: 134 MB of FC data, 0.318 compression, 0.532 seconds --> 253.226 MB/sec compression, 10.356 seconds --> 13.001 MB/sec decompression
Adds `snappy` compression to dossier.store.
Merge branch 'master' of github.com:dossier/dossier.store