New documentation, error function, and subprocess calling

This release adds an error function in case the model fails due to odd parameter combinations, for example, allowing the continuation of the calling process such as an optimizer. It also uses Python's relatively new subprocess.run() function now instead of the earlier subprocess.check_call() and subprocess.check_output().

The documentation was heavily rewritten. It changed from markdown format to reStructuredText and the hosting moved from ReadTheDocs to Github Pages. All docstrings were revisited and edited for better comprehension.