Redesign CMake syntax generator

The new approach is to use a trivial Python script, which uses a prepared YAML
data file and Jinja template to render the resulting syntax file.
Key features of the new implementation are:

• every command highlights only related named parameters -- e.g. add_library do not have TARGET named option, so it doesn't highlight in this context;
• new highlight classes have introduced to distinct property names, aliased (imported) targets, special non-named arguments;
• reuse RST syntax for comments;
• the input data now in VCS and trackable.