- Python 3 default binaries instead of leaving it open for interpretation
- Moved the readline comment up (seems important)
- Put a line about bash-completion
* Added individual pages for Windows, Linux and OSX with install
instructions.
* Dependencies were broken out into separate rst files and `include`d to avoid a lot of repetition
* Added instructions for adding `xonsh` to `/etc/shells` to standalone
rst file and `include`d them on OSX and Linux install pages