js literal with expression doesn't eval expression

[borkdude]

See babashka/nbb#57

[borkdude]

There is one thing left in this issue: currently we use clj->js and js->clj to convert between values, but these functions do a walk on the entire structure while #js only promises to do one level, so we should fix that compatibility.

[borkdude]

Currently #js also coerces values into JS objects, not good:

$ nbb -e '#js {:a :b}'
#js {:a "b"}