Sidebar changes based on screen size

When under ~360px screen size, opening the side menu causes the content
to collapse into a tight space. This change makes the sidebar overlay
the content rather than push it on anything under 360px.
Tided up theme CSS
Change size of when menu overlaps/pushes content
Updated readme to reflect latest changes/updates
Merge pull request #5 from Ehesp/dev

Pull in dev updates