Introduce templates for specific issue types (#8842)

This replaces the single github issue-reporting template with templates for the
following types of issues:

* Build issues
* Spack command errors
* Feature request

Each template includes suggestions which are generally useful for the type of
issue encountered.

.github/issue_template.md → .github/ISSUE_TEMPLATE/bug_report.md

-If you want to report a build error for some package, or a bug in core please use the following template as a guideline:
+---
+name: Bug report 
+about: Report a bug in the core of Spack (command not working as expected, etc.) 
 
------
-
-Summary
+---
 
-### Expected Result
 
-What you expected
+*Explain, in a clear and concise way, the command you ran and the result you were trying to achieve.
+Example: "I ran Spack find to list all the installed packages and..."*
 
-### Actual Result
 
-What happened instead
 
 ### Steps to reproduce the issue
 
@@ -20,6 +18,21 @@ $ spack <command2> <spec>
 ...
 ```
 
+### Error Message
+
+If Spack reported an error, provide the error message. If it did not report an error
+but the output appears incorrect, provide the incorrect output. If there was no error
+message and no output but the result is incorrect, describe how it does not match
+what you expect. To provide more information you might re-run the commands with 
+the additional -sd flags:
+```console
+$ spack -sd <command1> <spec>
+$ spack -sd <command2> <spec>
+...
+```
+that activate the full debug output. 
+
+
 ### Information on your system
 
 This includes:

.github/ISSUE_TEMPLATE/build_error.md

+---
+name: Build error 
+about: Some package in Spack didn't build correctly  
+
+---
+
+*Thanks for taking the time to report this build failure. To proceed with the
+report please:*
+1. Title the issue "Installation issue: <name-of-the-package>".
+1. Provide the information required below.
+1. Remove the template instructions before posting the issue.
+
+We encourage you to try, as much as possible, to reduce your problem to the minimal example that still reproduces the issue. That would help us a lot in fixing it quickly and effectively!
+
+
+---
+
+### Steps to reproduce the issue
+
+```console
+$ spack install <spec> # Fill in the exact spec you are using
+... # and the relevant part of the error message
+```
+
+### Platform and user environment
+
+Please report your OS here:
+```commandline
+$ uname -a 
+Linux nuvolari 4.15.0-29-generic #31-Ubuntu SMP Tue Jul 17 15:39:52 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
+$ lsb_release -d
+Description:	Ubuntu 18.04.1 LTS
+``` 
+and, if relevant, post or attach:
+
+- `packages.yaml`
+- `compilers.yaml`
+
+to the issue
+
+### Additional information
+
+Sometimes the issue benefits from additional details. In these cases there are
+a few things we can suggest doing. First of all, you can post the full output of:
+```console
+$ spack spec --install-status <spec>
+...
+```
+to show people whether Spack installed a faulty software or if it was not able to
+build it at all. 
+
+If your build didn't make it past the configure stage, Spack as also commands to parse 
+logs and report error and warning messages:
+```console
+$ spack log-parse --show=errors,warnings <file-to-parse>
+```
+You might want to run this command on the `config.log` or any other similar file
+found in the stage directory: 
+```console
+$ spack location -s <spec>
+```
+In case in `config.log` there are other settings that you think might be the cause 
+of the build failure, you can consider attaching the file to this issue.
+
+Rebuilding the package with the following options:
+```console
+$ spack -d install -j 1 <spec>
+...
+```
+will provide additional debug information. After the failure you will find two files in the current directory:
+
+1. `spack-cc-<spec>.in`, which contains details on the command given in input 
+    to Spack's compiler wrapper  
+1. `spack-cc-<spec>.out`, which contains the command used to compile / link the 
+    failed object after Spack's compiler wrapper did its processing 
+
+You can post or attach those files to provide maintainers with more information on what
+is causing the failure.

.github/ISSUE_TEMPLATE/feature_request.md

+---
+name: Feature request 
+about: Suggest adding a feature that is not yet in Spack  
+
+---
+
+*Please add a concise summary of your suggestion here.*
+
+### Rationale
+
+*Is your feature request related to a problem? Please describe it!*
+
+### Description
+
+*Describe the solution you'd like and the alternatives you have considered.*
+
+
+### Additional information
+*Add any other context about the feature request here.*
+
+
+-----
+
+
+If you want to ask a question about the tool (how to use it, what it can currently do, etc.), try the `#general` channel on our Slack first. We have a welcoming community and chances are you'll get your reply faster and without opening an issue.
+
+Other than that, thanks for taking the time to contribute to Spack!
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