Markdownified README.md

And corrected the link to the JetBrains logo, which did not work.
The "new" logo from their website does not provide the tag line, but is safe to link to according to https://www.jetbrains.com/company/press/materials.html (even though the dimensions shouldn't be changed).

As part of http://24pullrequests.com/
Correcting Skype link

A 'callto://'-link doesn't seem to work on GitHub...
Merge pull request #308 from habi/patch-1

Markdownified README.md