Support standard input formats for non-polynomial SDP

[vasdommes]

For simple non-polynomial SDPs, there are standard SDP formats, such as cbf (see https://cblib.zib.de/doc/format2.pdf) and dat-s (see http://opt.imi.kyushu-u.ac.jp/~fujisawa/sdpa_doc.pdf). SDPB could support these formats along with their gzip compressed versions, cbf.gz and dat-s.gz.

Supporting dat-s is also required for SDPLIB tests, see #105

Slack discussion: https://bootstrapcollab.slack.com/archives/CG450R9QX/p1703609519060999