Dev experience:
- CLJS now has source maps
- Devtools extension renders CLJS data in Chrome (et al) Devtools
- Use a debug build of CLJS in the tests
- Fixed line numbers and breakpoints being off-by-one in Devtools

CLJC infra:
- More robust direct approach to JS<->CLJS conversions, powered by
  Malli transformers.
- Powerful `define-getters-and-setters` macro to generate the accessors.