Distinguish JS scalar types for scene globals in functions (#979)
Distinguish JS scalar types for scene globals in functions (#979)

* Scene globals are put in JS context as distinct scalar types

* JS function results are coerced to booleans in filters

* Add note to distinguish Boolean values in JS property getter

cleeus/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,cleeus/tangram-es,cleeus/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,cleeus/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,cleeus/tangram-es,quitejonny/tangram-es