Minor improvement: replace JS emit with Fable AST
Minor improvement: replace JS emit with Fable AST

ncave/Fable,ncave/Fable,ncave/Fable,ncave/Fable,inosik/Fable,ncave/Fable,fable-compiler/Fable,ncave/Fable,fable-compiler/Fable,fable-compiler/Fable,inosik/Fable,ncave/Fable,fable-compiler/Fable,fable-compiler/Fable,fable-compiler/Fable,fable-compiler/Fable