Bug fixes in spherical diffuse interfaces

Some of the changes included in this release:

• Use double logarithmic scale for the integration of spherical diffuse interfaces, allowing for Runge-Kutta 4 integrator.
• A bug in the diffuse interface Green's function has been fixed.
• The layout of the installation for the Python scripts has been changed, addressing issue #116.
• The pcmsolver.py script/module was removed to address issues #111 and #112.

Read the change log for exhaustive information. Consult also the list of issues