Add systematic type-matrix and fuzz tests for expression functions - #350

Range.new/2 and first..last default to a step of -1 when last < first. Use Range.new(first, last, -1) or first..last//-1, or pass 1 if that was your intention

missing specification for function from_ucs4be/1

missing specification for function to_ucs4be/1

missing specification for function is_visible_ascii/1

missing specification for function is_visible_latin1/1

missing specification for function is_iso646_basic/1

missing specification for function is_ascii/1

missing specification for function is_latin1/1

missing specification for function is_bmpchar/1

missing specification for function is_unicode/1