chore(project): add issue templates

* bug report
* pr
* feature request

.github/ISSUE_TEMPLATE/BUG_REPORT.md

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+---
+name: Bug report
+about: Create a report to help us fix a library error
+---
+
+<!--
+
+Thanks for filing this bug report!
+
+Please take your time to provide the relevant context to your bug report. This helps us to process it and get it fixed, eventually.
+
+-->
+
+
+__Describe the Bug__
+
+A clear and concise description of what the bug is.
+
+
+__Steps to Reproduce__
+
+Steps to reproduce the behavior:
+
+1. do this
+2. do that
+
+If you report a modeling related issue, ensure you can reproduce it on [demo.bpmn.io](https://demo.bpmn.io/cmmn/new)
+
+When reporting a library error, try to build an example that reproduces your problem. You can use our playgrounds for [viewer](https://jsfiddle.net/x2doq4vn/) or [modeler](https://jsfiddle.net/nrko5hyt/) as a starting point or put a demo up on [GitHub](https://github.com/) for inspection.
+
+
+__Expected Behavior__
+
+A clear and concise description of what you expected to happen.
+
+
+__Environment__
+
+Please complete the following information:
+
+ - Browser: [e.g. IE 11, Chrome 69]
+ - OS: [e.g. Windows 7]
+ - Library version: [e.g. 2.0.0]

.github/ISSUE_TEMPLATE/FEATURE_REQUEST.md

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+---
+name: Feature request
+about: Suggest an idea or general improvement
+---
+
+<!--
+
+Thanks for filing this feature request!
+
+Please take your time to provide the relevant context
+that allows us to understand your proposal.
+
+-->
+
+
+__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 or screenshots about the feature request here.

.github/PULL_REQUEST_TEMPLATE.md

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+<!--
+
+Thanks for creating this pull request!
+
+Please make sure you provide the relevant context.
+
+-->
+
+__Which issue does this PR address?_
+
+Closes #