util.c: ignore trailing whitespace in parseindex

strtol already ignores leading whitespace so it doesn't make much sense
for us to worry about trailing whitespace.

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
util.c: tidy multiselect_parse

* loop over strtok_r results directly
* set default value upfront because it depends solely on the first value
* don't strtrim values, parseindex already takes care of any whitespace
  not removed by strtok_r
* add doxygen

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>