HOW_TO_TESTING.md

We must prevent uploads like v3.1.2 with careless, silly bugs. Here's a list of things which MUST be tested before every release:

1. Snippet execution: - both through hotkey and context menus
2. Mathomania - parentheses, exponents
3. Auto-Inserts
4. Snippet list display - through the issues#153 .txt file. It must exactly that display and executed snippet result - in both snippets and textareas - as it lists inside itself.

And on ALL these sites:

1. Gmail - Compose window, reply window - very frequently used, must support
2. stackoverflow.com/questions/ask - textareas
3. http://ckeditor.com/ - for iframes