Enhance the API with more functionality

[iimog]

As referees of our f1000 article note:

The API provided by BioJS is minimal. Notably, methods for partitioning, collapsing, transforming, filtering and subsampling are not present. While developers will be able to access sample or observation profiles as a whole, the current release of BioJS pushes much of the common manipulation logic onto the consumer of the library.

McDonald D and Bolyen E. Referee Report For: biojs-io-biom, a BioJS component for handling data in Biological Observation Matrix (BIOM) format [version 1; referees: 1 approved with reservations]. F1000Research 2016, 5:2348 (doi: 10.5256/f1000research.10362.r16546)

This can be changed by implementing the missing functions in this module:

• partitioning
• collapsing
• transforming
• filtering
• subsampling

[iimog]

Python docu for potential functions to implement:

• transform
• normalization
• presence/absence
• filter
• subsample
• reduce
• transpose
• partition
• collapse