Decay/Regenerate option for resources.
Allows entities to change their resource amount over time, possibly with some constraint.
This is a not-so-bare minimum, but can certainly be improved and/or extended later.
Part of: #1973
Original patch by: @smiley
Redone by: @Stan
Standing on the shoulders of giants: @Freagarach
(Revisions: 59; Inlines: 209)
Differential revision: D1718
Comments by: @Angen, @elexis, @Imarok, @Langbart, @nani, @Nescio, @smiley, @Stan, @wraitii