Document added System entries (GetEngineInteger and GetEngineString)

[ericoporto]

https://github.com/adventuregamestudio/ags-manual/wiki/System

  /// Gets a runtime engine value represented as integer by the given identifier; is meant for diagnostic purposes only
  import static int GetEngineInteger(EngineValueID value, int index = 0); // $AUTOCOMPLETESTATICONLY$
  /// Gets a runtime engine string by the given identifier; is meant for diagnostic purposes only
  import static String GetEngineString(EngineValueID value, int index = 0); // $AUTOCOMPLETESTATICONLY$

Examples of using it

int spritecachemax = System.GetEngineInteger(ENGINE_VALUE_I_SPRCACHE_MAXNORMAL);
int spritecachecurrent = System.GetEngineInteger(ENGINE_VALUE_I_SPRCACHE_NORMAL);
int spritecachepercent = spritecachecurrent * 100 / spritecachemax;
lblInfo.Text = String.Format("Sprite cache: %d / %d (%d%%)", spritecachecurrent, spritecachemax, spritecachepercent);

These were originally added in this PR adventuregamestudio/ags#2358

The enums are documented in #259

[ericoporto]

after this is in, put mention of it from System.DisplayFPS entry

[ivan-mogilko]

Added these:
https://github.com/adventuregamestudio/ags-manual/wiki/System#systemgetengineinteger

[ericoporto]

@ivan-mogilko we don't actually have any II (indexed integer) enums, do we?

[ivan-mogilko]

@ivan-mogilko we don't actually have any II (indexed integer) enums, do we?

Not right now, but this signature is reserved for that purpose.

[ericoporto]

I think it is better to either remove it or make a note that none of those are there yet, otherwise it looks like at least one of the enums must be a typo.

[ivan-mogilko]

Why remove it? It's a future compatible specification. We are saying that if such value IDs will be added, then they will use this pattern. It's a normal thing for expandable API, imo.

It's also mentioned in enum description here:
https://github.com/adventuregamestudio/ags-manual/wiki/StandardEnums#enginevalueid
and in script api header.

[ericoporto]

ok. Closing this as it is done.