Python wrapper can now output phase envelopes

import CoolProp
import matplotlib.pyplot as plt

HEOS = CoolProp.AbstractState('HEOS','Methane&Ethane')
for x0 in [0.2, 0.4, 0.6, 0.8]:
    HEOS.set_mole_fractions([x0, 1-x0])
    try:
        HEOS.build_phase_envelope("dummy")
    except: pass
    PE = HEOS.get_phase_envelope_data()
    plt.plot(PE.T, PE.p)

plt.xlabel('Temperature [K]')
plt.ylabel('Pressure [Pa]')
plt.tight_layout()
plt.show()
Clear the phase envelope before making the next one.

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Added files for LibreOffice to close https://github.com/CoolProp/CoolProp/issues/123

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>