Enhance error messages in pymob#159

flo-schu wants to merge 2 commits intodevflo-schu/pymob:devfrom

154-enhance-error-messages-to-be-more-informative-and-user-friendlyflo-schu/pymob:154-enhance-error-messages-to-be-more-informative-and-user-friendlyCopy head branch name to clipboard