Add ability to request multiple gridpoints for requests

Some users have requested the ability to request multiple gridpoints in a control record. 
A request might use comma separated values to specify location in ctl file. e.g.
`nlat=-10,30
slat=-30,10
wlon=-150
elon=-30`

Which could then be translated into json:
`nlat: [-10, 30],
slat: [-30,10],
wlon: [-150, -150],
elon= [-30, -30]`