support for the most basic cases of python 3.10's match syntax

Supported are, with basic type inference:
match "1 2 3".split():
  case [a, b]: ... # a, b are of type "str"
  case [a, b, c] as w: ... # w is of type "list of str"

(Other cases are parsed without complaint but have no type inference
or other special support. Variable declarations might be missing in some
cases.)