Optimising polarisation

I had a go with the examples and they work well (at least on Linux, not MacOS as per the other issue). Nice tool! One thing though that I'd like to look at is optimising reflectivity of a PBS at 1064 nm as well as between around 400-700 nm. I had a look at the optimize example and I can't see how to feed it polarisation requirements. The `diff_evo` function source doesn't appear to handle reflectivities/transmissivities per polarisation, unless I'm mistaken. Is this something that's supported or easy to add?

Start by reading the optimize example and the diff_evo function source to determine how optimization objectives currently represent reflectivity and transmissivity. Define how polarization-specific requirements for a PBS at 1064 nm and 400–700 nm should be expressed, then verify that the example can optimize those requirements on Linux and MacOS.

Written by the indexing model from the issue text.