Add sampgdk_InvokeNativeArray

while creating my own plugin i noticed it is in no way possible to call a native with an array of parameters. therefore i added a function. It does practically the same as sampgdk_InvokeNative, but without the use of a va_list.

sampgdk_InvokeNativeArray allows you to call a native function with an array of parameters.

Here follow a couple of example usages:
	char *info = new char[100];
	int len = strlen(info);

	void *args[2];
	args[0] = info;
	args[1] = &len;

	AMX_NATIVE getNetworkStats = sampgdk::FindNative("GetNetworkStats");
	sampgdk::InvokeNativeArray(getNetworkStats, "Sd", args);

	sampgdk::logprintf("stats: %s", info);

	// ... 

	float gravity = 0.8;

	void *args2[1];
	args2[0] = &gravity;

	AMX_NATIVE setGravity = sampgdk::FindNative("SetGravity");
	sampgdk::InvokeNativeArray(setGravity, "f", args2);

	// ...

	char *gamemode = "sampgdk";

	void *args3[1];
	args3[0] = gamemode;

	AMX_NATIVE setGameModeText = sampgdk::FindNative("SetGameModeText");
	sampgdk::InvokeNativeArray(setGameModeText, "s", args3);