Static init of the PS service

[Meziu]

Related to #43.

With these changes, the PS service will run for the whole app runtime, and be destroyed at the program's end. This way all code using libc::getrandom (and thus, also std::collections::HashMap) will work by default when using ctru::init at the start of the program.

A similar problem to this would still arise when using std::net and other networking functionality without using the Soc service, but that one is way heavier than PS and it's only needed in very specific cases the user should be aware of.

Edit: Also, since these changes rend the idea of a Ps struct both useless and detrimental (like closing the service while some program process still needs it), the functions have been made statics of the ctru::ps module and the struct has been removed.

@AzureMarker