add raise_error function

[rochacbruno]

this is taken from #43

Idea:

from pampy import match, _, raise_error

return match(x,
  1, "foo",
  2, "bar",
  _, raise_error(ValueError, "Message")
)

[blakev]

Alternatively, functionality like toolz.functoolz.excepts would delegate a case when an exception is raised.

See here, https://toolz.readthedocs.io/en/latest/_modules/toolz/functoolz.html#excepts