Create type keywords
Allow _CONSTANTS to start with _
Highlight constants before constructors
Move some keywords into @keyword.control

* str, list, etc. handled as @function.builtin and @type.builtin
* None and non-conforming type indentifiers as @type in type hints
* class identifiers treated as @type
* @constructor used for constructor definitions and calls rather than
  as a catch-all for type-like things
* Parameters highlighted
* self and cls as @variable.builtin
* improved decorator highlighting as part of @function

Re-ordering of some statements to give more accurate priority.

Python highlight improvements: type, parameter etc

Highting parameters with defaults and keyword arguments

Python highlight decorator attribute