Add issue templates used in GitHub

It's based on templates found in repo 'pmem/pmemstream'.

Author: lukaszstolarczuk

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Did you find a bug in UMF? Please let us know.
+labels: "bug"
+---
+<!--
+Before creating new issue, ensure that similar issue wasn't already created
+  * Search: https://github.com/oneapi-src/unified-memory-framework/issues
+
+Note that if you do not provide enough information to reproduce the issue, we may not be able to take action on your report.
+Remember this is just a minimal template. You can extend it with data you think may be useful.
+-->
+
+<!-- fill the title of issue with short description -->
+
+## Environment Information
+
+- UMF version (hash commit or a tag):                         <!-- fill this out -->
+- OS(es) version(s):                                          <!-- fill this out -->
+- kernel version(s):                                          <!-- fill this out -->
+- compiler, libraries, and other related tools version(s):    <!-- fill this out -->
+
+<!-- fill in also other useful environment data -->
+
+## Please provide a reproduction of the bug:
+
+<!-- fill this out -->
+
+## How often bug is revealed:
+
+(always, often, rare) <!-- pick one if possible -->
+<!-- describe special circumstances -->
+
+## Actual behavior:
+
+<!-- fill this out -->
+
+## Expected behavior:
+
+<!-- fill this out -->
+
+## Details
+
+<!-- fill this out -->
+
+## Additional information about Priority and Help Requested:
+
+Are you willing to submit a pull request with a proposed change? (Yes, No)  <!-- check one if possible -->
+
+Requested priority: (Showstopper, High, Medium, Low)                        <!-- check one if possible -->

.github/ISSUE_TEMPLATE/feature.md

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+---
+name: Feature
+about: Request a feature/enhancement
+labels: "enhancement"
+---
+
+<!-- fill the title of your feature/enhancement -->
+
+## Rationale
+
+<!-- fill this out -->
+
+## Description
+
+<!-- fill this out -->
+
+## API Changes
+
+<!-- fill this out, if needed -->
+
+## Implementation details
+
+<!-- fill this out if possible -->
+
+## Meta
+
+<!-- fill this out -->

.github/ISSUE_TEMPLATE/question.md

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+---
+name: Question
+about: Do you have question regarding UMF? Don't hesitate to ask.
+labels: "question"
+---
+
+<!-- fill the title with short version of your question -->
+
+## Details
+
+<!-- fill this out -->