Modernize build/CI, support SourceMod 1.13, deprecate ForceHeartbeat

Rework the build and CI: swap to SourceMod's safetyhook-based CDetour and
drop the vendored CDetour/asm sources, the old Makefile, Travis config, and
buildbot perl scripts. Add GitHub Actions building and releasing x86 and
x86_64 against SM 1.12 and 1.13, plus dependabot. Split the Windows and Linux
packages and tidy naming.

Gate IPluginManager::FindPluginByContext on the extension API version so the
extension builds against both SM 1.12 (API 8) and 1.13 (API 9), and shim
DETOUR_CREATE_STATIC_FIXED over the address overload safetyhook exposes.

Deprecate SteamWorks_ForceHeartbeat: newer Steamworks SDKs removed
ISteamGameServer::ForceHeartbeat, so make the native a no-op and mark it
deprecated in the include.

configure.py

@@ -19,8 +19,6 @@ if ambuild_version.startswith('2.1'):
 	sys.exit(1)
 
 run = run.BuildParser(sourcePath=sys.path[0], api='2.2')
-run.options.add_argument('--hl2sdk-root', type=str, dest='hl2sdk_root', default=None,
-		                   help='Root search folder for HL2SDKs')
 run.options.add_argument('--mms-path', type=str, dest='mms_path', default=None,
                        help='Path to Metamod:Source')
 run.options.add_argument('--sm-path', type=str, dest='sm_path', default=None,
@@ -31,8 +29,5 @@ run.options.add_argument('--enable-debug', action='store_const', const='1', dest
                        help='Enable debugging symbols')
 run.options.add_argument('--enable-optimize', action='store_const', const='1', dest='opt',
                        help='Enable optimization')
-run.options.add_argument('-s', '--sdks', default='all', dest='sdks',
-                       help='Build against specified SDKs; valid args are "all", "present", or '
-                            'comma-delimited list of engine names')
 run.options.add_argument('--target', default=None, help='Override the default build target')
 run.Configure()