Add basic ReHLDS and ReGameDLL support (#417)

* Add ReHLDS API files and its dependencies

Note: This has been stolen from ReAPI AMXX module and modified/adjusted to match AMXX existing includes and to provide as less dependencies as possible as well

* Add the necessary files to get ReHLDS interface

* Split SV_DropClient into pre/post code

* Init ReHLDS API and add SV_DropClient hook

* Add Cvar_DirectSet hook and adjust code with helpers

Note: we don't need to split code here. This is pretty much the naive and straight way, but fairly enough for our case. If it happens we got a lot more hooks, we may consider to use some class to manage better the things.

* Move platform and interface stuff in their own files in public directory

* Make sure to init cvar stuff after ReHLDS

* Add ReGameDLL API files and its dependencies in cstrike module

* Init ReHLDS in cstrike module and adjust code

Note: About cs_uset_set_model(). ReHLDS API doesn't offer a way to know directly the precached models, so instead of looping through all the ressources, the models list is saved one time at map change into a hashmap.

* Init ReGameDLL and adjust code

* Fix linux compilation

* Init ReGameDLL in fakemeta module and adjust code

* Rename /reapi directory to /resdk to avoid confusion

* Retrieve gamerules pointer through InstallGameRules in fakemeta module

* Retrieve gamerules pointer through InstallGameRules in cstrike module

Note: actually gamerules is not used if regamedll is enabled, but it could be used in future natives.

* Fix a typo when ReGameDLL is not enabled

* Fix missing interface check for ReHLDS.

I'm pretty sure I was checking at the very first since I worked first on vanilla version of engine, looks like change has been lost.

modules/fakemeta/AMBuilder

@@ -10,6 +10,7 @@ binary.compiler.defines += [
 binary.sources = [
   '../../public/sdk/amxxmodule.cpp',
   '../../public/memtools/MemoryUtils.cpp',
+  '../../public/resdk/mod_regamedll_api.cpp',
   'dllfunc.cpp',
   'engfunc.cpp',
   'fakemeta_amxx.cpp',