New, more flexible, parser context datatype that includes and extends

the previous flags allowForest and allowVarRef.
Added binary operator (work in progress).
Better implementation of +=,-=,*=, and /= (new) operators.

scanner.go

@@ -149,6 +149,8 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			if next, _ := scanner.peek(); next == '*' {
 				scanner.readChar()
 				tk = scanner.fetchBlockComment()
+			} else if next, _ = scanner.peek(); next == '=' {
+				tk = scanner.moveOn(SymSlashEqual, ch, next)
 			} else if next == '/' {
 				scanner.readChar()
 				tk = scanner.fetchOnLineComment()
@@ -590,7 +592,7 @@ func (scanner *scanner) fetchString(termCh byte) (tk *Token) {
 	}
 	if err != nil {
 		if err == io.EOF {
-			tk = scanner.makeErrorToken(errors.New("missing string termination \""))
+			tk = scanner.makeErrorToken(errors.New(string(termCh)))
 		} else {
 			tk = scanner.makeErrorToken(err)
 		}