add support for JSON_TABLE

[lovasoa]

see https://dev.mysql.com/doc/refman/8.0/en/json-table-functions.html
and
https://modern-sql.com/blog/2017-06/whats-new-in-sql-2016#json_table

Fixes sqlpage/SQLPage#146

Closes #1019

[coveralls]

Pull Request Test Coverage Report for Build 7091199686

• 93 of 105 (88.57%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.004%) to 87.71%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser/mod.rs	44	47	93.62%
src/ast/query.rs	23	32	71.88%

Files with Coverage Reduction	New Missed Lines	%
src/ast/query.rs	1	83.08%

Totals
Change from base Build 7009122777:	0.004%
Covered Lines:	18085
Relevant Lines:	20619

---

💛 - Coveralls

[lovasoa]

@alamb : I'm adding more and more json-related features to SQLPage, and users are starting to complain about failed query parsing in MySQL. It would be great if we could get this merged :)

[alamb]

@alamb : I'm adding more and more json-related features to SQLPage, and users are starting to complain about failed query parsing in MySQL. It would be great if we could get this merged :)

Thanks @lovasoa -- I will try and review this in the next day or two

[alamb]

Looks good to me -- thank you @lovasoa

[lovasoa]

Thanks @alamb ! This will be very useful in sqlpage !