Allow both linestyle definition "accents" and dash-patterns as linestyle...

... for collection, lines and patches.

(code & tests)

see. #2136

This is a minimal patch. It seems to me that the linestyle handling could get some more cleanup.
e.g. in lines.py the drawing is handed over to some `_draw_xxx` methods, those are almost only stubs changing the name of the linestyle
?! What text do you mean, the parameter description, type or name? What main description of the docs, the one of Line2D? The tables of keyword arguments actually do not work correctly with numpydoc. Is that what you mean?