Autocomplete tag parameters

[wolflu05]

With inspect we can introspect available parameters for a function. This can be used to introspect the available parameters. Additionally docstrings that comply to formats like reSt, google, ... can be used to extract the description for it. These can then be autocompleted when typing.

Additionally it would be great if we could assign certain parameters some functions. E.g. to make auto completion of templates/static files with custom tags possible.