dashes are just a more limited form of linestyles. Actually, they are no more than:

    def set_dashes(self, seq):
        if seq == (None, None) or len(seq) == 0:
            self.set_linestyle('-')
        else:
            self.set_linestyle((0, seq))

I propose to soft-deprecate dashes in favor of linestyle. Dashes are redundant and thus only increase the API complexity without any benefit. OTOH I don't think we should deprecate dashes because there might be quite a bit of code out there using it.

Specific actions for this task:

• linestyle should directly accept a dash pattern. - It currently only accepts (offset, dash_pattern).
• Change all internal code and examples to use set_linestyle.
• In set_dashes, recommend to use set_linestyle instead.
• Add an API change note along the lines.