Adding some missing curves & common NIST aliases

Morning Dazoe,

This pull request adds secp192r1 and secp256r1 to the ECCurve hash obj, and also a few common NIST aliases (nistp192~521), because choosing from the list of 30+ curves is a bit intimidating. Alas, can't go wrong with NIST recommendations. Only main.cc is changed.

PS: better documentations would be much appreciated.

Best,

xkxx