Add concept of "entity cost" to perks

Add a field to perk config indicating how costly every perk can be on the entity count.

Suggestion 1

Perks will have a new field called entity_cost which tells RTD roughly how many perk-spawned entities are possible to exist at one time. It can be written in the form of a formula which includes perk settings as variables. For example:

Smite: "entity_cost" "1" // proxy entity for effects
A Call Beyond: "entity_cost" "%amount% * 6 / %rate%" // rough estimate given the amount and spam potential

Suggestion 2

Perks will have a new field called cost which specifies the name of the function that RTD can call in order to retrieve the entity cost of a perk. The function will accept the Perk instance from which it can read its variables.

Smite: "cost" "Smite_Cost"

int Smite_Cost(const Perk perk) { return 1; } // proxy entity for effects

A Call Beyond: "cost" "ACallBeyond_Cost"

int ACallBeyond_Cost(const Perk perk) 
{
// rough estimate given the amount and spam potential
return perk.GetPrefCell("amount") * Ceil(6.0 / perk.GetPrefFloat("rate"));
}

Use case

If anyone is crazy enough to run RTD on a 60 or 100 player servers, there can be a ConVar sm_rtd2_entity_cost_limit (default 99) which will disable every perk beyond the specified limit. Setting this ConVar will show exactly which perks were disabled including their cost.

Implementation notes

[S1] Supporting formulas and variables can be a quite a burden on implementation. I need to look at every perk but hopefully everything will be implementable without worrying about order of evaluation (so no addition/subtraction or braces).
[S1] Division by 0 will fail the parsing and result in 99 entity cost.
[S2] Lack of the cost specification will result in it being 0.
[S2] If cost is specified but not found, it will result in it being 99 and a message in the error log.
Every float returning operation must be rounded up in order to avoid zero-ing out the result. For example 1 / %rate% must be 1 regardless of how high rate is.
Non positive values should be specified as 99 and throw an error in the log.

Phil25 / RTD