add float support to scanner and parser
add semantic checking & generation for floats
tidy up type checking functions
Merge branch 'master' into floats

Conflicts:
	compiler/generate.ml
	compiler/parser.mly
	compiler/sast.mli
	compiler/sast_printer.ml
	compiler/semantic_check.ml
	compiler/translate.ml
Merge pull request #71 from rapid-lang/floats

Float support