add github templates for PR and Issues

Author: Kiko Fernandez Reyes

.github/ISSUE_TEMPLATE.md

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+Make sure the following boxes are checked before creating an issue:
+
+- [] State the problem
+- [] Specify the compiler's branch and make sure it is on top of `development`
+- [] Use a Github label if possible
+- [] Try to provide a minimal example that reproduces the error

.github/PULL_REQUEST_TEMPLATE.md

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+Make sure these boxes are checked before submitting your pull request:
+
+- [] Description of the pull request stating the problem and the solution
+- [] Tests (if applicable)
+- [] Documentation (if applicable)