Update issue templates

Author: chschulte

.github/ISSUE_TEMPLATE/bug-report.md

@@ -0,0 +1,17 @@
+---
+name: Bug Report
+about: Create a bug report to help us improve Gecode
+
+---
+
+**Describe the Bug**
+
+Please provide a clear and concise description of what the bug is.
+
+**To Reproduce**
+
+Try to explain how to reproduce the bug.
+
+**Gecode and Platform Configuration**
+
+Please describe which version of Gecode you use, on which operating system, and with which C++ compiler (including its version).

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,17 @@
+---
+name: Bug report
+about: Create a report to help us improve
+
+---
+
+**Describe the bug**
+
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+
+Try to explain how to reproduce the bug.
+
+**Gecode and Platform Configuration**
+
+Please describe which version of Gecode you use, on which operating system, and with which C++ compiler (including its version).

.github/ISSUE_TEMPLATE/request-a-feature-in-gecode.md

@@ -0,0 +1,15 @@
+---
+name: Request a Feature in Gecode
+about: Suggest a new feasture
+
+---
+
+**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 Feature**
+
+Please describe the feature in as much detail as you can.
+
+**Why Is the Requested Feature Useful?**
+
+Please argue why the feature is useful to you and _others_.