chore: add issue templates

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a report to help us improve
+
+---
+
+### Environment
+
+* Elixir & Erlang/OTP versions (`elixir --version`): 
+* Operating system: 
+
+### Current behavior
+
+Include code samples, errors and stacktraces if appropriate.
+
+### Expected behavior

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for this project
+
+---
+
+**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.