lang: Detect windows style CR and return a better error

If you get a sneaky \r in your code, the error just looks like
whitespace, so this way we can warn you explicitly.

lang/lexer.nex

@@ -384,8 +384,12 @@
 			yylex.pos(lval) // our pos
 			s := yylex.Text()
 			lp := yylex.cast()
+			e := ErrLexerUnrecognized
+			if s == "\r" { // windows!
+				e = ErrLexerUnrecognizedCR
+			}
 			lp.lexerErr = &LexParseErr{
-				Err: ErrLexerUnrecognized,
+				Err: e,
 				Str: s,
 				Row: yylex.Line(),
 				Col: yylex.Column(),

lang/lexparse.go

@@ -46,6 +46,7 @@ const (
 // These constants represent the different possible lexer/parser errors.
 const (
 	ErrLexerUnrecognized      = interfaces.Error("unrecognized")
+	ErrLexerUnrecognizedCR    = interfaces.Error("unrecognized carriage return")
 	ErrLexerStringBadEscaping = interfaces.Error("string: bad escaping")
 	ErrLexerIntegerOverflow   = interfaces.Error("integer: overflow")
 	ErrLexerFloatOverflow     = interfaces.Error("float: overflow")