Add Support for Recursive CTEs

[rhanqtl]

See https://jakewheat.github.io/sql-overview/sql-2016-foundation-grammar.html#with-clause

Fixes #277

[coveralls]

Pull Request Test Coverage Report for Build 300120070

• 29 of 30 (96.67%) changed or added relevant lines in 4 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.2%) to 92.018%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/query.rs	6	7	85.71%

Files with Coverage Reduction	New Missed Lines	%
src/test_utils.rs	1	80.77%

Totals
Change from base Build 288554202:	0.2%
Covered Lines:	4784
Relevant Lines:	5199

---

💛 - Coveralls

[rhanqtl]

error: match expression looks like `matches!` macro
   --> src/tokenizer.rs:385:60
    |
385 |                       let s = peeking_take_while(chars, |ch| match ch {
    |  ____________________________________________________________^
386 | |                         '0'..='9' | '.' => true,
387 | |                         _ => false,
388 | |                     });
    | |_____________________^ help: try this: `matches!(ch, '0'..='9' | '.')`
    |
    = note: `-D clippy::match-like-matches-macro` implied by `-D warnings`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#match_like_matches_macro

[nickolay]

Thanks, this PR looks great, apart from a couple of nits below.

Regarding the clippy error, it's probably a lint enabled in a new clippy version? Would you like to fix it while you're at it?

[nickolay]

Thanks again!