1. Fix an issue in ParseCode method 2. Add new additional Inspect method

[kzvankovich]

1. Fix an issue in ParseCode method :
   During exchanging code for an access token I got the following error: redirect_uri isn't an absolute URI. Check RFC 3986.
2. Add new additional Inspect method:
   added Inspect Session access token functionality

[huandu]

Hi @kostjazvankovich , thanks for your fix!

I merge your changes with following modifications.

• Remove the second parameter of app.ParseCode and use app.RedirectUri instead. Per facebook's document, redirect uri must be the set to the exact value in the app's configuration. So it should be considered as an app config like app id and secrect.
• use gofmt -tabs=false -tabwidth=4 -w . to format code. You used a different way to format code. It makes me a hard time to see diffs.

Again, thanks for your contribution!