add Config for extensible configuration

[programmerjake]

Adds a extensible method for setting demangling configuration.

Using {:#} as the format string still works for both a less verbose method and for backwards compatibility by acting as if with_hash was set to false.

See also #36 (comment)

I also made some items pub(crate) instead of pub since they weren't externally visible

[programmerjake]

Btw, if you add an fn display_with_config(self, Config) -> impl fmt::Display you could call .to_string() on that without this crate knowing about String.

That would be either demangle_with_config(mangled, config).to_string() or demangle(mangled).with_config(config).to_string().

[eddyb]

Oops, I misremembered the fmt_with_config I suggested as public API, sorry.

[alexcrichton]

Thanks for the PR! I'm sort of confused though as to what purpose this is serving? Is this fixing an immediate bug?

[programmerjake]

Thanks for the PR! I'm sort of confused though as to what purpose this is serving? Is this fixing an immediate bug?

It's a new feature upon which more configuration options can be added, so it's not really a bug fix.

[alexcrichton]

Ah ok, in that case I would prefer to not land this since we do not have a future feature in mind at this time. When that comes about I think it makes sense to design the scaffolding then to fit the feature, rather than trying to build the scaffolding now and hope the feature fits in the future.

[programmerjake]

ok, seems reasonable