(/=) SQLLexer

(+) „Desugar“ Syntax for table renaming. Example „CaseDetail c“ is
equivalent to „CaseDetail as c“. Doing this simplifies the grammar for
the parser.
(/=) Modify test to better test renaming, as SQL is case insensitive
(/=) SQLLexer : Consider the fact that SQL syntax is case insensitive

This is accounted for by passing the case insensitive flag (?i) to the
Pattern. We can write the rules just accounting for a-z now, and FROM,
WHERE, … now also tokenize correctly.
Additionally, the matches (except literals) are converted to lowercase
for later convenience (semantic is case insensitive, so having it all
in lowercase is handy).