Also make it a little less allocation-heavy by tweaking the API to
encourage incremental building of the key and incremental destruction as
we walk throughout the configuration tree.

Rewrite helpers like `get_bool` to use `get::<Option<Value<bool>>>`
instead of duplicating the logic that's already with the typed access of
configuration. This is more along the effort to centralize all
deserialization of configuration into typed values instead of using
ad-hoc accessors in a number of locations.

This callsite doesn't need the full power of `get_list`, knowing the
definition path of each element along the list.

Gives us one nice place to access and document all HTTP-related configuration

Going through and removing users of raw `get_*` functions!

Less need for `get_bool` and friends!

Add a typed structure which lists all `build` key configuration
throughout Cargo.

No need for lots of extra helpers/parsing when using serde!