proposal: disallow operator "=>" and use it for named parameters

Hello

two years a operator "=>" is marked as deprecated (from PostgreSQL 9.2).

Isn't time to use it for named parameters now (for PostgreSQL 9.5) ?

I am sending a implementation where syntax based on "=>" symbol is second
(but preferred) variant of ":=" syntax .. syntax ":=" will be supported
still.

Here is a patch

comments, notices?

Regards

Pavel