Re: jsonpath

Attached 15th version of the patches.

There are changes only in jsonpath lexer:
  * added single-quoted strings
  * added escape sequences \v, \', \xXX, \u{...}

It's all required by ECMAScript standard (ECMA-262), from which SQL/JSON
standard adopts lexical rules.


Also, the documentation has been moved into a separate patch
(see https://www.postgresql.org/message-id/732208d3-56c3-25a4-8f08-3be1d54ad51b%40postgrespro.ru).

-- 
Nikita Glukhov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company