0.6.0

• Upgraded to Spark 2.2.1. Added VersionShims to allow for Spark 2.1.x backwards compatibility.
• Introduced separate rasterframes-datasource library for hosting sources from which to read RasterFrames.
• Implemented basic (but sufficient) temporal and spatial filter predicate push-down feature for the GeoTrellis layer datasource.
• Added Catalyst expressions specifically for spatial relations, allowing for some polymorphism over JTS types.
• Added a GeoTrellis Catalog DataSource for inspecting available layers and associated metadata at a URI
• Added GeoTrellis Layer DataSource for reading GeoTrellis layers from any SPI-registered GeoTrellis backend (which includes HDFS, S3, Accumulo, HBase, Cassandra, etc.).
• Ability to save a RasterFrame as a GeoTrellis layer to any SPI-registered GeoTrellis backends. Multi-column RasterFrames are written as Multiband tiles.
• Addd a GeoTiff DataSource for directly loading a (preferably Cloud Optimized) GeoTiff as a RasterFrame, each row containing tiles as they are internally organized.
• Fleshed out support for MultibandTile and TileFeature support in datasource.
• Added typeclass for specifying merge operations on TileFeature data payload.
• Added withTemporalComponent convenince method for creating appending a temporal key column with constant value.
• Breaking: Renamed withExtent to withBounds, and now returns a JTS Polygon.
• Added EnvelopeEncoder for encoding JTS Envelope type.
• Refactored build into separate core and docs, paving way for pyrasterframes polyglot module.
• Added utility extension method withPrefixedColumnNames to DataFrame.