admin: Set up new issue templates (#1981)

It had escaped my notice that last month, GitHub ended support for a
single ISSUE_TEMPLATE.md, and now only supports an ISSUE_TEMPLATE
directory with individual templates. I can't imagine the engineering
reason for not being able to continue to support having just one
template as always.

Anyway, so this PR conforms to what they support, by copying (and
lightly modifying) the issue templates that OIIO has used for some
time.

Signed-off-by: Larry Gritz <[email protected]>

Author: lgritz

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,45 @@
+---
+name: Bug report
+about: I think I have identified a legit bug and can describe it.
+title: "[BUG]"
+labels: ''
+assignees: ''
+
+---
+
+Note: The prompts below are just to help you formulate a good and actionable
+request. Feel free to deviate from this format or to delete this text and
+write free-form if you prefer.
+
+**Describe the bug**
+
+A clear and concise description of what the bug is. What happened, and
+what did you expect to happen instead.
+
+
+**OSL version and dependencies**
+
+* OSL branch/version: 
+* OS: 
+* C++ compiler: 
+* LLVM version: 
+* OIIO version: 
+
+
+**To Reproduce**
+
+Steps to reproduce the behavior:
+1. Do this...
+2. Then this...
+3. Then THIS happens (reproduce the exact error message if you can)
+4. Whereas I expected this other specific thing to happen instead.
+
+
+**Evidence**
+
+- Error messages (paste them here exactly)
+- Example shader code (if applicable)
+
+
+**IF YOU ALREADY HAVE A CODE FIX:** There is no need to file a separate issue,
+please just go straight to making a [pull request](https://github.com/AcademySoftwareFoundation/OpenShadingLanguage/pulls).

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,24 @@
+---
+name: Build problems
+about: I'm having trouble building OSL. Help!
+title: "[BUILD]"
+labels: ''
+assignees: ''
+
+---
+
+**PLEASE DO NOT REPORT BUILD TROUBLES AS GITHUB "ISSUES" UNLESS YOU ARE RALLY SURE IT'S A BUG**
+
+The best way to get help with your build problems is to ask a question on the
+[osl-dev developer mail list](https://lists.aswf.io/g/osl-dev). For quick
+questions, you could also try the [ASWF Slack](https://slack.aswf.io)
+`#openshadinglanguage` channel.
+
+When you email about this, please attach one or both of the following:
+1. The full verbose build log, which you can create like this:
+   ```make clean ; make VERBOSE=1 > build.log```
+2. The `CMakeCache.txt` file from your build directory.
+
+If you are pretty sure that you have identified a **BUG** or other actual
+problem with the OSL build scripts and you can describe how to reproduce it,
+please file a [bug report issue](https://github.com/AcademySoftwareFoundation/OpenShadingLanguage/issues/new?template=bug_report.md).

.github/ISSUE_TEMPLATE/build_problem.md

@@ -0,0 +1,25 @@
+---
+name: Feature request
+about: I have a concrete idea about how to improve OSL.
+title: "[FEATURE REQUEST]"
+labels: ''
+assignees: ''
+
+---
+
+Note: The prompts below are just to help you formulate a good and actionable
+request. Feel free to deviate from this format or to delete this text and
+write free-form if you prefer.
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context about the feature request here.

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,28 @@
+---
+name: Question
+about: How do I...  I need help with...
+title: "[HELP]"
+labels: ''
+assignees: ''
+
+---
+
+**PLEASE DO NOT ASK USAGE QUESTIONS USING GITHUB "ISSUES"**
+
+If you are pretty sure that you have identified a **BUG** in OSL, please file
+a [bug report issue](https://github.com/AcademySoftwareFoundation/OpenShadingLanguage/issues/new?template=bug_report.md).
+
+But if you are just asking a question:
+* How do I...?
+* I need help with...
+* Am I doing something wrong?
+* I can't build OSL
+
+For anything of this nature, the best way to get help using OSL is to ask a
+question on the [osl-dev developer mail list](https://lists.aswf.io/g/osl-dev).
+For quick questions, you could also try the [ASWF Slack](https://slack.aswf.io) `#openshadinglanguage` channel.
+
+Please check the [documentation](https://docs.openshadinglanguage.org) first;
+you may find the answer more quickly than you can get your question answered
+on the mail list.
+

.github/ISSUE_TEMPLATE/question.md

@@ -495,10 +495,11 @@ Contact & reporting problems
 ----------------------------
 
 Simple "how do I...", "I'm having trouble", or "is this a bug" questions are
-best asked on the [osl-dev developer mail
-list](https://lists.aswf.io/g/osl-dev).
+best asked on the [osl-dev developer mail list](https://lists.aswf.io/g/osl-dev).
 That's where the most people will see it and potentially be able to answer
-your question quickly (more so than a GH "issue").
+your question quickly (more so than a GH "issue"). For quick questions, you
+could also try the [ASWF Slack](https://slack.aswf.io) `#openshadinglanguage`
+channel.
 
 Bugs, build problems, and discovered vulnerabilities that you are relatively
 certain is a legit problem in the code, and for which you can give clear