Add generic `call` function which uses the command interface

[Phil25]

Perk config is very versatile, but it can be even more so.

Example

There could be an unused-by-default call function which is able to execture commands provided via perk's settings, for example:

"myslapperk"
{
	"name"			"My Slap Perk"
	"good"			"0"
	(...)
	"settings"
	{
		"command"	"sm_slap"
		"arg1"		"%target%" // %target% gets replaced with user ID player who rolled the perk
		"arg2"		"100" // slap damage
	}
	"call"			"CustomCommand_Call"
	"init"			"CustomCommand_Init"
}

Overview

The command can be provided via the command setting and its arguments through consecutive argN settings. The function called CustomCommand_Call will parse and build a command that is run on the server, targeting the player who rolled this particular perk.

%target% will be replaced with the user ID of a player by RTD, to make sure addressing is unique and not name-dependent. Furthermore, %target% can be specified in any argument, since it's up to the command to define which argument is the target.

CustomCommand_Init will verify whether the command is valid and is safe (see section below) to run while the config is parsed. This is helpful for debugging because you can see a message in the server logs whether you configured something incorrectly.

Security

Running server commands in an unsolicited way is bad. CustomCommand_Call will always check flags of the provided command. Commands will the following flags should error out without being executed:

1. kick
2. ban
3. unban
4. changemap
5. cvar
6. config
7. password
8. rcon
9. root