First attempts to adding linux support. It's broken.
Implement mouse down and mouse up for Linux
Initial implementation of scrolling

It is unclear how to control scroll speed with PyUserInput, so for
now the calculated scroll velocities are unused.
Removed x64 Linux libraries (user should supply x86 or x64 as for Windows)
Updated README
Merge pull request #7 from pythonian4000/linux

Add Linux support. Thanks to Òscar and Jack.