Typical bugs

Add section with typical bugs met when implementing given specification described on article. Do it as third tab along with table of content and notes.

Drawing

On article editor add ability to add section which allow for drawing diagrams like in Google Docs or Word. It should show canvas nested in article. Available components on drawing canvas: rectangle, ellipse, text label, straight line, free hand drawing, arrow. They should be draggable, rotatable, with changing colors.

this section should be added when user selects proper icon from toolbar or when user types / and popup menu appears.