Bash installer

Hi,

I've started working on a bash installer to simplify the installation of phpbrew.

What it does:

* Detect OS
* Install dependencies depending on the OS
* `phpbrew init`
* If ran by `sudo`, will install phpbrew to `/usr/local/phpbrew`
* Mostly unit tested

It's almost done (I need to test it, add some missing dependencies installation procedure).

Would you be interested in this (should I pull request somewhere)?