Combine interpreter state variables into state record #est

This is mainly just to make handling of them easier and not so much
for hiding internal fields which are explicitly accessed when
necessary. It will also make it easier to add new fields when
necessary.
Make it work for loading files as well
Fix error handling to use state and use try/catch instead of catch
Convert ets interface to new state record
Make sure findall drops all new bindings and revert to old bindings

Fixes #50.