0.1.8 Release: custom save functions and duplicate names

This is tmt release 0.1.8. What's new?

• You can now specify custom save functions (for instance, save your objects with numpy instead of pickle);
• You can now have and handle duplicate experiment names (experiments are still uniquely identified by a UUID);
• tmt_recorder now has a description argument. Use it to give a (possibly long) description of your experiment;
• when searching in the TUI, you can now see the date saved.

Documentation is available on readthedocs.