[WIP] Class-based parsing

New version of  PR #8. 

Don't merge yet.

This code implements an OOP approach to timestream parsing. This will be the only supported way of parsing TimeStreams. It will transparently handle v1 (AKA folder) or v2 (i.e. netCDF4/HDF5) timestream formats.

This is work in progress, APIs will almost certainly change. See [util/class_parser_demo.py](https://github.com/kdmurray91/timestreamlib/blob/oop/util/class_parser_demo.py) for a demo.

I'll push to this branch as I make changes. Keep an eye on this PR if you want to keep track of what I'm up to WRT this @chuong @timescience @Joelgranados.

K