Extend Windows Overlay code and clean it up.

Extend to handle library freeing.
Codeformatting and -cleanup, robustness, and make debugoutput more consistent.

* Indroduce hook for freeing loaded DLLs.
This separates logic between loading and freeing, leading to adjustments to
the recently introduced checks for freed DLLs.
* In HardHook::reset() do a clean and complete reset rather than minimal.
* Memvarinitialisation in HardHook
* Remove logically unused variable bPresenting in d3d9.cpp (always false)
* In d3d10.cpp prefix debugoutput with D3D10 consistently; no more DXGI
which is ambiguous with a d3d11 file that also uses DXGI.
* Consistently use ods instead of fods in the overlay files.
Not in HardHook yet, as that class is used in the Mumble client as well atm
* Fix forwarded return value types (LONG to ULONG)
* TODOs for hook-call-logic in multiple places
* Commenting, formatting and scope / order adjustments
* Introduce variables with constant values (replacing magic/undescriptive constants/numbers)
Code refacs; fix typo and adjust texts

* fix typo
* debug text adjustments
refacs: more elaborative Varnaming; codeformatting
* Commenting, varnaming, fix indent

* commenting and adjusting debug output
* more descriptive varnaming
Refac: Use constant to check return value

* mmap supposedly returns MAP_FAILED on errors, which is supposedly
defined in <sys/mman.h>, which is already being included in this file.