Update debian packaging.

GitHub: Add an issue template

GitHub: Add a template for issues submitted, .github/issue_template.md.
I hope people could provide more needed information when reporting
issues after we provide a number of fields to fill and some extra
instructions in the template, to reduce the time wasted on the issues
because of insufficient information.

See: https://help.github.com/articles/creating-an-issue-template-for-your-repository/

Second beta release

- Add --unredir-if-possible-delay and --unredir-if-possible-exclude .

- Add --xinerama-shadow-crop .

- (Presumably) more reliable focus detection.

- Fix some numeric locale related issues.

- Fix some --opacity-rule related issues.

- Add D-Bus option stoppaint_force.

- Add condition matching target `x2` and `y2`.

- Add workaround for insane window type changes.

- Support CPPFLAGS.

First beta release.

Perhaps not so perfect, but I hope nothing terribly wrong, either.