Tokenize SQL before parsing and preserve tokens for recompilation

[katzyn]

SQL is now tokenized before parsing. Tokens are preserved for second parse if SQL contains an error. Tokens are also stored in prepared commands for re-use if their recompilation is needed. Forward scans now can simply iterate over already known tokens.

Handling of supplementary Unicode characters in identifiers and whitespace is improved.

In long tests with looped TestScript performance on Java 8 is improved by about 1.2–1.5% on warm JVM. Because this test doesn't use recompilation actively, most of its commands don't produce errors, and it contains only few commands where complex forward scans are required I hope we shouldn't have performance degradation caused by these complications with tokens.

I think both Parser and Tokenizer can be improved in the future, but changes in them should be carefully tested, because actual performance impact may be very surprising.