Feature request: option to avoid embedding message/field names as plaintext in prost-derive (Message derive)

[h3zh1]

Hi, and thanks for the great library!

I've noticed that when using:

#[derive(Clone, PartialEq, Eq, Hash, ::prost::Message)]
pub struct Foo { ... }

the generated code from prost-derive causes both the message name and
its field names to be embedded as plaintext in the compiled binary.

Looking at prost-derive (currently 0.14.1), in try_message the
derive macro generates:

const STRUCT_NAME: &'static str = stringify!(#ident);

and later in merge_field:

error.push(STRUCT_NAME, stringify!(#field_ident));

All stringify!(...) calls produce &'static str constants, which end
up in the final binary.

• It leaks internal schema names such as user_password,
  internal_token, etc.
• It eases reverse engineering.