change issue templates

[lgsmith]

I'd like to change default issue template to use more markup from markdown. Instead of having the various sections of an issue report be a boldface title and then a sentence in plaintext explaining what should go there, I think that the title should have a section marker, or if that's too large then a subsection marker, and the instructions should be in a comment. This would look something like the following (note that I escaped the leading comment mark so that you could see what I figured the comments ought to read like):

Describe the bug

<!---A clear and concise description of what the bug is.--->

To Reproduce

<!---Steps to reproduce the behavior. A bulleted or numbered list is preferred.--->

Expected behavior

<!---A clear and concise description of what you expected to happen.--->

LOOS version and platform

<!---Which version you're running, on what OS, and how it was built (e.g. conda, system libraries, manually installed dependencies). If you're working from a publicly posted commit, consider linking that here.--->

Additional context

<!---Add any other context about the problem here.--->

I believe that this will make it easier for people to read the reports, because it'll make skimming a bit better (you get the cross-lines from the use of section, which I like) and it'll get rid of the prompt text that is currently co-mingled with the answers when some users fill these out. I tend to delete it when I file issues, but I've noted that others don't necessarily.

[agrossfield]

Addressed by 43b33d6

[agrossfield]

Finally went back and changed the prompts to comments.