Generalize production of Ergo runtime

[jeromesimeon]

The Ergo runtime is a patched-up version of the Q*cert one. It is composed of vanilla JavaScript functions without module layout for node consumption. We should improve upon this in several ways:

• [x] Automate the production of the runtime from Q*cert itself so changes/fixes there are propagated to Ergo automatically
• [x] Allow the runtime generation to be parameterized by foreign type libraries (e.g., various support for dateTime)
• [x] Generalize the runtime generation so it works for both browser and node

[jeromesimeon]

Should be done on new JavaScript backend, see #191

[jeromesimeon]

Quite a lot of improvements are already available in the release-1.0 branch. Some additional work to reduce the footprint of the runtime, and leverage the new Imp intermediate language would still be useful. I'm leaving this open for the time being.

[jeromesimeon]

Most of this is done in release-1.0 branch. One more item to add before we can close this issue:

• [ ] Do not duplicate the Qcert runtime in ./runtime/javascript, but import it from the now published Qcert library