Make some basic url shortcuts to the API docs.

The following urls now redirect to the relevant documentation on the
wiki:

    phantomjs.org/api
    phantomjs.org/api/webpage
    phantomjs.org/api/system
    phantomjs.org/api/fs
    phantomjs.org/api/webserver
    phantomjs.org/api/child_process

I often find myself struggling to remember the exact url for each page of documentation. Hopefully this will help make the documentation more accessible.