HDI Updated to Include Dynamic Pressure Unit Conversion

I have added the ability to dynamically convert the display between different pressure units.  The HDI currently uses Pa, kPa, and psi.  But my MPR library supports several other pressure units, including Pa, kPa, psi, atmospheres (both standard and technical) Torr, Bar, Bayre, inHg, mmHg, inH2O, mmH2O and others.

I added a Temperature unit symbology to the library, too.  This allows you to fetch the symbol for the the pressure you are using by function call.

Since I am using an absolute pressure transducer, I can easily convert between pressure units by a simple calculation using the conversion factors of the source unit and the target unit.