#269: Update CONTRIBUTING guidelines, add PR and issue templates

- Add issue templates for bugs, translations and new snippets

- Add PR templates for general purpose, new snippets and translations

.github/ISSUE_TEMPLATE/bug.md

@@ -0,0 +1,25 @@
+---
+name: Bug report
+about: Bug template
+title: 'Fix ...'
+labels: 'bug'
+
+---
+
+<!--
+Hi, thanks for submitting a bug. We appreciate that.
+
+But, we will need some information about what's wrong to help you.
+-->
+## What's wrong
+
+<!-- Describe what is not working. -->
+
+## How it should work?
+
+<!-- Describe how it should work. -->
+
+## Checklist before calling for maintainers
+
+* [ ] Have you checked to ensure there aren't other open [Issues](../../../issues) for the same problem?
+

.github/ISSUE_TEMPLATE/new_snippet.md

@@ -0,0 +1,23 @@
+---
+name: New snippet
+about: New snippet template
+title: 'New snippet: ...'
+labels: 'new snippets'
+---
+
+<!--
+Hi, thanks for submitting a new snippet. We appreciate that.
+
+But, we will need some information and (optionally) explanation to accept it.
+-->
+## Description
+
+## Snippet preview
+
+## Checklist before calling for maintainers
+
+* [ ] Have you checked to ensure there aren't other open [Issues](../../../issues) for the same update/change?
+* [ ] Have you checked that this snippet is not similar to any of the existing snippets?
+<!--Explanation is optional. You may suggest a snippet without deepp understanding of its behavior.-->
+* [ ] Have you added an `Explanation` section? It shall include the reasons of changes and why you'd like us to include them
+

.github/ISSUE_TEMPLATE/translation.md

@@ -0,0 +1,13 @@
+---
+name: Translation
+about: New translation template
+title: 'Tranlate to ...'
+labels: 'translations'
+
+---
+
+<!--Hi, thanks for suggesting a new translation. We appreciate that.-->
+## Checklist before calling for maintainers
+
+* [ ] Have you checked to ensure there aren't other open [Issues](../../../issues) for the same tranlation?
+* [ ] Do you wish to make a translation by yourself?