Complete AST parsing for most SELECT clauses

[machow]

Most of these just involve removing the keyword

• [x] FROM list of tables: SELECT a FROM b, c
• [x] WHERE
• [x] GROUP BY
• [x] UNION
• [x] ORDER BY
• [x] OFFSET (not in parser, see issue #45 )

(bonus: HAVING, WINDOW, FETCH, FOR)

[machow]

see issue #44 for ORDER BY parsing issues