AttributeRef/StateRef: fix two small bugs

Attribute ref was setting the debug info, even if not provided, at
object creation. This led to misleading behavior for UnnamedAttributeRef
objects when the position was changed. E.g., it would be created as
pos=6, debug=$6, then pos would get changed to 2. Now, leave debug_info
alone if not provided and add the $ on print.

UnnamedStateAttributeRef did not implement all needed methods
UnnamedStateAttributeRef: test

It was not covered by the existing tests
Merge pull request #285 from uwescience/minor-bugfixes

AttributeRef/StateRef: fix two small bugs
myrialang: support new CountAll aggregator

Do not have to pretend it reads -zsh instead.
aggregate.py: minor cleanup
typo fix
aggregate: replace stupped evaluate with NotImplementedError

When I read the comment I was confused as to how that could be the
correct behavior. But actually, this function is never called by the
tests. Replace the stub with a NotImplementedError, which I think makes
more sense.
aggregate: cleaup std calculation
sum: reimplement evaluate_aggregate
Merge pull request #286 from uwescience/minor-agg-fixes

Minor agg fixes
basic uda parser support

However it just gets turned into a StatefulApply
groupby: rename fields as prep for UDAs
stash