Remove `raise Exception(..)`
Many of these should be `AstNotImplementedError`.

`raise()` related ones could possibly be merged into a helper, and if it is absolutely only catching coding errors, a new exception type might be more appropriate, e.g. `AstInvalidBuiltinInvocation`.  But IMO we shouldnt be detecting bad code except in very limited scenarios (e.g. ctypes integer bounds we are doing, but mypy rejects those anyway per https://github.com/adsharma/py2many/issues/359 ).  If we're detecting bad code, we need to somehow create that bad code in order to test that part of the code, and such bad code  cant be run on Python to demo that the test case is valid, and that seems like lots of brittle busy-work.

```py
❯ GIT_PAGER=cat git grep -n --after-context=1 'raise.*Exception'
py2many/clike.py:610:        raise Exception("Unimplemented")
py2many/clike.py-611-
--
py2many/clike.py:613:        raise Exception("Unimplemented")
py2many/clike.py-614-
--
py2many/clike.py:616:        raise Exception("Unimplemented")
py2many/clike.py-617-
--
pydart/plugins.py:105:            raise Exception(
pydart/plugins.py-106-                "encountered range() call with unknown parameters: range({})".format(
--
pygo/plugins.py:103:        raise Exception(
pygo/plugins.py-104-            "encountered range() call with unknown parameters: range({})".format(vargs)
--
pyjl/plugins.py:99:        raise Exception(
pyjl/plugins.py-100-            "encountered range() call with unknown parameters: range({})".format(vargs)
--
pyjl/transpiler.py:177:        raise Exception(
pyjl/transpiler.py-178-            "encountered range() call with unknown parameters: range({})".format(vargs)
--
pykt/plugins.py:101:        raise Exception(
pykt/plugins.py-102-            "encountered range() call with unknown parameters: range({})".format(vargs)
--
pynim/plugins.py:47:        raise Exception(
pynim/plugins.py-48-            "encountered range() call with unknown parameters: range({})".format(vargs)
--
pyrs/plugins.py:84:        raise Exception("read() with more than one argument")
pyrs/plugins.py-85-
--
pyrs/plugins.py:93:        raise Exception("write() with more than one argument")
pyrs/plugins.py-94-
--
pyrs/plugins.py:120:        raise Exception(
pyrs/plugins.py-121-            "encountered range() call with unknown parameters: range({})".format(vargs)
```