Added MXCAL support

* hipsr-mbcal.py -- Takes an observation of 1934-638 and computes noise diode temperatures in Jy
* hipsr-converter.py -- Added support to load custom noise diode temperatures
* sdfits.py -- Added support to use custom noise diode cal files instead of library version

Signed-off-by: Danny Price <dan@thetelegraphic.com>
Documentation for generateSDFitsFromHipsr

Signed-off-by: Danny Price <dan@thetelegraphic.com>