Feature request: allow user to specify destination dir for solutions plots

[Greg Sleap]

Currently hyperdrive writes out the 2 .png files to the path where hyperdrive is run from. It would be nice to tell hyperdrive where to write the files,
e.g. to get the plots written to /tmp you might implement something like this:

hyperdrive solutions-plot  --metafits 1234567890_metafits.fits --output-dir /tmp 1234567890_solutions.fits

or alternatively, write them to the same folder that the solutions file (bin, fits, rts) is (which is passed in as the first positional parameter).

p.s. this is a very low priority request :-)