Create issue template

[Painatalman]

Why

Issue templates can structure common issue types (like error reports and feature requests), thus making them easier to both read and write.

How

We should consider what type of templates to create, and what sections to include in each of them.
For error reports (like issue #29), I usually follow this structure:

• title with (summed up) error message
• error summary and message (untitled)
• steps to reproduce
• installed software (and packages)
• possible cause or possible solution (if any)
• suggestions