Support for additional data formats from UC data explore

[pmslavin]

This issue is to implement Reader classes for the dataset storage formats identified during the UC data explore.

These include:

1. TMY3: Typical Meteorological Year format
2. GeoPackage: a SQLite-based format
3. ASCII-Grid: The ASCII (as opposed to binary) version of ESRI Grid
4. CSV: With potentially variation in separator, encoding, etc.

A first step in this process is to identify existing support in libraries for parsing these formats.