Issue template for different categories

[marcozzxx810]

We should setup different templates for different issue.

We can follow scikit learn for now

The categories can be

• Bugfix
• feature
• doc improvements

[foarsitter]

People don't follow them anyway but I'm happy to review a PR.

[marcozzxx810]

@foarsitter why say so? When user create issue, they need to choose the best issue template.

Why I am proposing so? Many issue here are opened, which we are not sure it is a real problem.

We need to manage the issue better so that potential contributor can work on.

[foarsitter]

Just my personal experience with issue templates. I'm not against improving things and looking forward to a pull-request!