Revert 'add context and flag argument to js_newstate' commit.
The context argument just adds clutter. The flag which was intended
for JS_DEBUG and/or JS_STRICT shouldn't be necessary.
js_newcfunction and js_newcconstructor need an extra argument, the
name of the function to use in stack traces.
Separate literal/interned and garbage collected string types in js_Value.
js_pushintern/js_tointern are convenience functions to push/pop strings and
automatically intern them (so that the string pointers are guaranteed to be
stable).
js_pushliteral should push stable strings (either interned or actual literals).
js_pushstring will copy the string into garbage collected memory.
The pointer returned by js_tostring is guaranteed to be stable only for as long as
the stack slot it came from remains untouched.
Some uses will always cause a string to be interned:
* Using it as a property name.
* Wrapping it in a new String() object.
* Strings returned by toString().
ToPrimitive must not clobber the stack, so the result has to be unrooted.
* Numbers converted to strings (by js_tostring)
Likewise, we have nowhere to store the temporary string here.
Passing in a scratch buffer to js_tostring could help this problem.
Mostly an issue with array accesses (OP_GETPROP, etc) so an auxiliary
function and we don't have to clutter the API needlessly.
js_newuserdata(J, tag, ptr) creates a userdata object, wrapping the ptr.
It takes the prototype for the new object from the top of the stack, just
like js_newcconstructor does.
js_touserdata(J, tag, idx) extracts the userdata pointer. Throws a
TypeError if the object is not a userdata object with a matching tag.
js_isuserdata(J, tag, idx) checks if a value on the stack is a userdata
object with a matching tag.
