added readme file
Tuned boss appearance probabilty.

This restores the merge of the no-companies branch by reverting commit bd57c486e8b4ba9c29504c1929d6e2b2072875a3.
Spring cleaning: removed unnecessary files and fixed formatting of main js script
Added a "Professional Invaders" title on top of the game page
Tuned down probability for boss to appear
Added a simple splash screen if users are not logged in
Splash screen thumbnail, footer and share buttons
Lowered the boss probability (again)
moved github ribbon and improve font sizes on the footer
Fixed the ribbon URL
Added "Read More" link
Merge branch 'master' into gh-pages