RowValue derive macro

[nothingelsematters]

This is our solution for #49. It contains a new derive crate with a RowValue derive macro.

A macro usage example:

#[derive(RowValue)]
struct TestStruct {
    #[row_value(rename = "fifth")]
    first: String,
    second: i64,
    #[row_value(with = "some::path::custom_big_decimal_parser")]
    third: BigDecimal,
    fourth: Option<String>,
}

This would expand into an oracle::RowValue implementation which constructs a structure as follows:

TestStruct {
    first: row.get("fifth")?,
    second: row.get("second")?,
    third: some::path::custom_big_decimal_parser(row, "third")?,
    fourth: row.get("fourth")?,
}

[kubo]

@nothingelsematters
Thanks for making pull request.

Could you change as follows?

1. Rename the crate name from rust-oracle-derive to oracle_procmacro.
   The crate name of rust-oracle is oracle. So the name of the new crate should be similar.
   In addition the crate may contain not only derive macros but also other procedural macros in future.
2. Add [workspace] and an empty line as follows at the top of Cargo.toml at the top level directory.

   [workspace]
   
   [package]
   name = "oracle"
   ...
   

   In https://doc.rust-lang.org/cargo/reference/workspaces.html:

   An empty [workspace] table can be used with a [package] to conveniently create a workspace with the package and all of its path dependencies.