Changes hotloader to be a lib rather than a bin so that client
libraries can list it as a dependency and compile it automatically.
Removes the hard-coded path to the game dll from loader in favor of
having the client lib pass it in when starting the loader.
renames polygon_rs crate to polygon in order to avoid breakage with
hotloading. It probably should just be polygon, anyway, so not a big
deal.
Adds a null module to the stopwatch crate so that client code can
disable usage of stopwatch without removing all calls to its code.
Adds "timing" and "hotloading" features to gunship to allow client
code to enable and disable timing critical sections and hotloading
respectively.
Fixes hotloading by using a modified version of the type name when the
hotloading feature is enabled. When hotloading is disabled the TypeId is
used instead because it is cheaper at runtime.