errors not being shown when something fails

[woloski]

This error
https://github.com/auth0/wp-auth0/blob/master/WP_Auth0.php#L167

And this error
https://github.com/auth0/wp-auth0/blob/master/WP_Auth0.php#L179

Are only accesible by looking at the apache log and sometimes that's not available. Show those errors as part of the error page.

[mgonto]

This is related to #22

[glena]

I'm not sure where these lines were pointing, with the last changes seems to be moved.
I think I'm logging all posible errors #22

[glena]

should be ready