Added an ability to specifiy additional paths to search for coding standards

Hi there.

The idea behind this is to allow to specify additional paths that CS will scan for standards.
It's a proposition. Tell if you are positive about these changes I see if I can work something out.

Default standards are always loaded.
Added options: --standards-path=path1,path2,path3

There is a small issue with options - the order matters and I think its a general issue.
phpcs -i --standards-path=dir1

... will not display standards in "dir1". Instead use:

phpcs --standards-path=dir1 -i