fixes run's single method (#85)

* Fixes #82
* Changes:
    * input arguments now reflects the changes made to read_molecule_file in #84
    * Writing of pKa file is now optional (default behaviour has been kept). This will be particularly 
       useful downstream where we would just want to have access to the MoleculeContainer object.
     * new test_run file specific for testing run.
* add tests
* add docs

docs/source/conf.py

@@ -73,3 +73,6 @@ html_theme = 'sphinx_rtd_theme'
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
 html_static_path = ['_static']
+
+# Enable intersphinx mapping
+intersphinx_mapping = {'python': ('https://docs.python.org/3', None)}