Changes for JOSS reviewing process

[michael-petersen]

There are several adjustments and improvements to make as part of the JOSS review process; this branch will handle them in one place.

[michael-petersen]

First, a quality-of-life improvement with adding an issue template.

[michael-petersen]

Some draft paper updates to resolve #97.

Anything else we should add, @The9Cat?

[The9Cat]

That seems good to me. I suppose we could add the original S-L description in the 1999 paper, but the recent other paper(s) are more complete and refer to the 1999 paper, and that paper doesn't describe EXP per se.