Generate standard ISSUE_TEMPLATE and PULL_REQUEST_TEMPLATE files

[Daniel Bachhuber]

It would be helpful to include .github/ISSUE_TEMPLATE and .github/PULL_REQUEST_TEMPLATE files for each package.

See:

• https://help.github.com/articles/creating-an-issue-template-for-your-repository/
• https://help.github.com/articles/creating-a-pull-request-template-for-your-repository/