Most of our uses of source extent were cargo cult programming. The source extent was seldom and inconsistently used. Instead, layers can now be configured with an extent, and layer renderers limit rendering (and data requests) to the layer extent.
For vector sources, the `getExtent` method returns the extent of currently loaded features (this was the case before and after this change). For tile based sources, we will likely want to allow easy construction of tile grids based on an extent (this is not possible before or after this change, but could be added later).
This change adds a stability value to the api annotation, with
'experimental' as default value.
enum, typedef and event annotations are never exportable, but
api annotations are needed there to make them appear in the
docs.
Nested typedefs are no longer inlined recursively, because the
resulting tables get too wide with the current template.
The projection option for vector file sources currently has no good meaning. The reprojectTo option is used to set the projection for cached features. This change makes it so the projection option is used for this purpose. The getProjection method (not currently exported) can then be used to get the cached feature projection.
This also removes the default of 'EPSG:3857' for vector file sources. If a projection is not configured, features will not be transformed.
