* pywellen: make var and scope carry a pointer to the hierarchy

* pywellen: implement variable and scope access similar to vcdvcd

* pywellen: change iterator

* wip: better hierarchy iterators

* fix uses of all_vars and all_scopes

* implement and test item iterator

* hierarchy: add all_items for scope

* pywellen: remove VarIter and ScopeIter

* pywellen: one test passes

* pywellen: expose more meta data

* pywellen: pass most tests again

* pywellen: all tests are passing

* pywellen: test change iterator

* hierarchy: improve name lookup

* wip: signal slice

* pywellen: slice into changes

* pywellen: add variable indexing

* stream: re-use header parsing from viewer

* pywellen: lazily load actual signal data

* automatically convert signal values into most apropriate type

* pywellen: wip streaming

* pywellen: simple streaming works

* wip: thread errors through

* stream: finish error threading

* pywellen: wip stream time changes

* pywellen: stream time steps working

* stream: fix some tests

* stream: fix tests