Updates to installation and packaging pages

Includes:

* Slightly fuller install instructions for Ubuntu and others
* Changes to the Windows and OSX packaging pages, primarily to prevent the packager from including the entire source folder in the distributed output
Nop, pip cannot work with osx, as we don't ship it within the portable distribution. More than that, the rest of the osx packaging ask the user to go to the pyinstaller directory. Could you adjust it?