Add max and min to expressions

[cswhite2000]

Adds max and min as functions that can be used in <set/> actions

Example:

<set var="player_score" value="min(player_score,3)"/>
or
<set var="player_score" value="max(player_score,10)"/>

[Pablete1234]

Just to leave a record of it, we discussed trying to support things like max(a, b, c, d) but Exp4j expects a specific number of parameters for a function, no support for variable amount of args.

Would be great to long-term have that tho, but for the time being 2-arg is the best we can do