Add Git and GitHub templates (#19)

* Add GitHub templates

* Add git commit template

Author: yim-lee

.github/PULL_REQUEST_TEMPLATE.md

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+_[One line description of your change]_
+
+### Motivation:
+
+_[Explain here the context, and why you're making that change. What is the problem you're trying to solve.]_
+
+### Modifications:
+
+_[Describe the modifications you've done.]_
+
+### Result:
+
+_[After your change, what will change.]_

dev/git.commit.template

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+One line description of your change
+
+Motivation:
+
+Explain here the context, and why you're making that change.
+What is the problem you're trying to solve.
+
+Modifications:
+
+Describe the modifications you've done.
+
+Result:
+
+After your change, what will change.