Implementation of Peng-Robinson equation of state.

Implemetation of Peng-Robinson equation of state

added factories for FlowDevice and Wall objects

Updating `thermo/PengRobinsonMFPT` class addition.

-Adds `test/data/co2_PR_exmample.cti` for testing.
-Corrects typo in `src/thermo/PengRobinsonMFTP::setSpeciesCoeffs`
-Minor formatting changes (indentations)
-Change how `Vroot_` is initialized.

Updating ctml_writer.py to include acentric_factor
Updating a typo in PengRobinsonMFTP.cpp

Updating ctml_writer.py to add units for b_coeff

Updating ctml_writer.py to add units for b_coeff with correct
indentation

Correcting a mistake in the getActivityCoefficient subroutine

Updating PengRobinson_Test.cpp with accurate hard-coded values

Adding a test getPressure in PengRobinsonMFTP_Test.cpp file

Fixing tabs and spaces

Replacing 'doublereal' with 'double'

Fixing tabs and spaces in the CTI file

Adding comments and renaming few parameter names

Fixing tabs and spaces

Following modifications in the code are performed:

1. Fixing typos
2. Adding more detailed documentation
3. Deleting redundant variables

Fixing typos and comments in the cubic solver

Fixing typos in PengRobinsonMFTP.h

Replacing (molecularWt/rho) calculations by molarVolume() function

Modifying tests with tighter tolerances

Modifying comments and reference for cubic solver

Replacing sqrt(2) with math constant M_SQRT2

Modification in cubic solver with additional comments and removal of
redundant code