Make getApplicationAccessToken public

For posting apprequests, we need to use the application access token
not the user one. It is easy to specify this in the parameters to api
call except that the method to retrieve it is protected. I can see no
obvious reason why.
Marked deprecated methods with @deprecated.
Constructor reuses $state local variable pulled from persistent storage.
Merge pull request #8 from dmnc/master

Make getApplicationAccessToken public
Merge pull request #10 from dharkness/deprecations

Add replacement method to @deprecated tags