Reflect all (most) properties and methods available in mapnik-core

[artemp]

Good bindings should strive to expose as much of the underlying library functionality as reasonable. This issue is to track progress adding missing properties and methods available in https://github.com/mapnik/mapnik

Map

Layer

properties

• [x] name
• [x] src
• [x] styles
• [x] datasource
• [x] minimum_scale_denominator
• [x] maximum_scale_denominator
• [x] queryable
• [x] clear_label_cache
• [x] active
• [ ] cache_features
• [ ] group_by
• [ ] buffer_size
• [ ] comp_op
• [ ] maximum_extent
• [ ] opacity

methods

• [x] describe
• [ ] envelope
• [ ] reset_maximum_extent
• [ ] reset_buffer_size

Datasource

Image

TODO : add more

ref #786