implement compiler directives

[Kacarott]

[JohanWiltink]

in no particular order: #import filename.lc - import external code ( may need facility for specific imports renaming or namespacing ) #export binding-name - export a subset of defined bindings #no-export binding-name - export a subset of defined bindings, inverted logic #constant binding-name - protect a binding from being overwritten in the current scope #define binding-name JS-code - define a magic binding