Correlation Compound

Added a data table for vapour pressure correlations, uses the correlation: lnP = c1 + (c2/T) + c3*ln(T) + c4*T^c5

The CorrComp class now returns saturation properties using the correlation, also can look up datab
Copy and Init for Compounds

Instead of copying everything __init__ just copies critical properites, name, id, and cas number.  Otherwise the namespace of a compound can get crazy cluttered, if it is initialized from another compound of a different class.

Now the copy routine copies.

Also Compounds can get values by cmp[key], and set values by cmp[key] = value (forgot to add that before)

Both of the above copy numpy arrays, using the array.copy() method.