Added equals assignment operator

The set phrase will be removed and just replaced with a single
equals sign. Double equals will be used for comparison. This will
be much easier to understand.

lexer/lexer_test.go

@@ -155,7 +155,8 @@ func TestTokenizeAll (test *testing.T) {
 		quickToken(2, TokenKindPercentAssignment, nil),
 		quickToken(1, TokenKindTilde, nil),
 		quickToken(2, TokenKindTildeAssignment, nil),
-		quickToken(1, TokenKindEqualTo, nil),
+		quickToken(1, TokenKindAssignment, nil),
+		quickToken(2, TokenKindEqualTo, nil),
 		quickToken(2, TokenKindNotEqualTo, nil),
 		quickToken(1, TokenKindLessThan, nil),
 		quickToken(2, TokenKindLessThanEqualTo, nil),