Suppor postgres TRUNCATE syntax

[tobyhede]

Correctly parses the following pg options:

ONLY
RESTART IDENTITY | CONTINUE IDENTITY 
CASCADE | RESTRICT 

And supports providing a list of table names

TRUNCATE table_a, table_b, table_c

[coveralls]

Pull Request Test Coverage Report for Build 10674424966

Details

• 75 of 83 (90.36%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.003%) to 89.254%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser/mod.rs	19	20	95.0%
src/ast/mod.rs	16	19	84.21%
tests/sqlparser_postgres.rs	40	44	90.91%

Files with Coverage Reduction	New Missed Lines	%
src/ast/mod.rs	1	81.46%

Totals
Change from base Build 10653671802:	0.003%
Covered Lines:	28804
Relevant Lines:	32272

---

💛 - Coveralls

[alamb]

Thanks @tobyhede -- looks good to me.

I'll plan to leave this open for a few days to give @iffyio and others a chance to review as well if they want

[iffyio]

LGTM!

[alamb]

Thanks again @tobyhede @iffyio