ENH: subsample can now do by_id
MAINT: minor refactor of subsample code
ENH: method to generate unlimited subsamples
DOC: addressing comments by @adamrp and @ElDeveloper
DOC: addressing comments by @adamrp
DOC: changelog additions, comment by @ElDeveloper
DOC: bumping iterations
Merge pull request #486 from wasade/subsample_ids

Randomly subsample by ID, and generate unlimited random subsamples