some missing documentation for arb_mat #1640
Description
After looking at this message on flint-devel , a very quick check showed that there are several arb_mat functions that are not documented, beyond the one mentioned in that message. At least several swap functions, and find_pivot_partial. I am not familiar with arb_mat code: is this on purpose? if not, I can take some time to properly identify and add the missing documentation pieces.