Rendering

API for starting template rendering from arbitrary XML

This API accepts arbitrary well-formed XML as rendering data and starts document rendering asynchronously. The XML root element is preserved in the rendering data. How the XML becomes rendering data: - Element and attribute names are lower-cased and every character outside `[a-zA-Z0-9_]` becomes `_`. Two sibling elements or two attributes on the same element whose names collapse onto the same key are rejected with HTTP 400 instead of being merged. Elements are compared by namespace and local name, so the same element written with two prefixes bound to the same namespace stays one repeated element. - An element that occurs **once** becomes an object or string, an element that occurs **more than once** becomes a list. Templates using repeating sections (`rr_`) must therefore be built against a payload that really repeats. - Attributes are collected under `_attributes`, mixed text next to child elements under `_text`. - DTD-declared internal entities are resolved; external entities are never loaded. - The top-level key `or` is reserved for Output.Rocks control data. A root element that maps to `or` is rejected with HTTP 400.