namespace sts::ams -> ams::exosphere, ams::.

This is to facilitate future use of ams:: namespace code in
mesosphere, as we'll want to include ams::util, ams::result, ams::svc...

Because I was working on multiple things at once, this commit also:
- Adds wrappers for/linker flags to wrap CXX exceptions to make them
  abort. This saves ~0x8000 of memory in every system module.
- Broadly replaces lines of the pattern if (cond) { return ResultX; }
  with R_UNLESS(!cond, ResultX());.
- Reworks the R_TRY_CATCH macros (and the result macros in general).

This implements waitable management for Events (and
implements Events). It also refactors PM to use new
Event/Waitable semantics, and also adds STS_ASSERT
as a macro for asserting a boolean expression. The
rest of stratosphere has been refactored to use
STS_ASSERT whenever possible.

Specifying 0 as the initial entry of a structure is a C-ism. C++ permits
using an empty set of braces to signify the same behavior, silencing
missing initializer warnings.