added `rename_all` container attribute for enums and structs

[JaydenElliott]

Related issue: #934

Adding a rename_all attribute to a struct or enum will rename the container's fields/variants according to the rule specified. Similar to serde's rename_all but for use with ToSql and FromSql.

This removes the need to manually rename each field/variant before inserting/selecting from postgres (especially useful with enums, who's naming standards differ from rust).

Supported rules:

• "lowercase"
• "UPPERCASE"
• "PascalCase"
• "camelCase"
• "snake_case"
• "SCREAMING_SNAKE_CASE"
• "kebab-case"
• "SCREAMING-KEBAB-CASE"

No external dependencies introduced. Case conversion code from serde was used.

Thanks @jakubadamw for the test cases from #952

[sfackler]

Can you also update the documentation here? https://github.com/sfackler/rust-postgres/blob/master/postgres-types/src/lib.rs

LGTM otherwise

[JaydenElliott]

Can you also update the documentation here? https://github.com/sfackler/rust-postgres/blob/master/postgres-types/src/lib.rs

LGTM otherwise

@sfackler Documentation added, see f4b181a20180f1853351be53a32865b6209d0ab4

[JaydenElliott]

can this be approved + merged @sfackler ?

[kitsuniru]

we waiting for u, @sfackler

[sfackler]

Thanks! Sorry for the delay