Vector enhancements

Added

• Raster client can now handle arbitrarily large numbers of tiles generated from a shape using the new iter_dltiles_from_shape() method which allows you to iterate over large numbers of tiles in a time- and memory-efficient manner. Similarly the existing dltiles_from_shape() method can now handle arbitrarily large numbers of tiles although it can be very slow.
• Vector client upload_features() can now upload contents of a stream (e.g. io.IOBase derivative such as io.StringIO) as well as the contents of a named file.
• Vector FeatureCollection add() method can now handle an arbitrary number of Features. Use of the upload_features() method is still encouraged for large collections.
• Vector client now supports creating a new product from the results of a query against an existing product with the create_product_from_query() method. This support is also accessible via the new FeatureCollection.copy() method.
• XYZTile GeoContext class, helpful for rendering to web maps that use XYZ-style tiles in a spherical Mercator CRS.

Changed

• Tasks client FutureTask now instantiates a client if none provided (the default).
• Catalog client methods now properly handle add_namespace parameter.
• Vector Feature now includes valid geojson type 'Feature'.
• Tasks client now raises new GroupTerminalException if a task group stops accepting tasks.
• General documentation fixes.