PEAR package

Onion (PEAR Package builder/bundler) https://github.com/c9s/Onion can build PEAR package automatically,

so I think php-webdriver can be distributed through PEAR channel very easily. (can use symfony/Pirum)

only 3 things need to do with this:

1. Move source files into src/ directory
2. Define 4 lines package.ini file
3. Use Pirum to release this package on PEAR channel.