feat: Allow backslash escaping inside double quotes

Examples:

- ?col=in.("Double\"Quote")
- ?col=in.("Back\\slash")

Backslashed chars get passed as is

- ?col=in.("\a\b\c") = ?col=in.(abc)

CHANGELOG.md

@@ -13,6 +13,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
    + Enables calling a function with a single json parameter without using `Prefer: params=single-object`
    + Enables uploading bytea to a function with `Content-Type: application/octet-stream`
    + Enables uploading raw text to a function with `Content-Type: text/plain`
+- #1938, Allow escaping inside double quotes with a backslash, e.g. `?col=in.("Double\"Quote")`, `?col=in.("Back\\slash")` - @steve-chavez
 
 ### Fixed