Function: count_chosen

DOC_MSE_VERSION: since 0.3.7

--Usage--
> count_chosen(choices: some_string, some_multiple_choice_value)

Coint the number of choices that are selected in a [[type:value#multiple_choice|multiple choice value]].

If the @choices@ parameter is given then only choices from that list are counted.

--Parameters--
! Parameter	Type				Description
| @input@	[[type:string]]			Multiple choice value to look in.
| @choices@	optional [[type:string]]	A comma separated list of choices to look for.

--Examples--
> count_chosen("")                                 ==  0
> count_chosen("red")                              ==  1
> count_chosen("red, green")                       ==  2
> count_chosen("red, green", choices: "red,blue")  ==  1

--See also--
| [[fun:chosen]]		Is a given choice selected in a multiple choice value?
