Add try/catch for parsing FB responses

Sometimes Facebook returns HTML instead of JSON when their API fails. 

See: http://bit.ly/ZKtEX5

In these situations we should try to catch and handle the JSON.parse error. 
It happens quite infrequently so even in the FB bug report it is difficult 
to reproduce consistently. 

Improve comments for try/catch around JSON.parse
improve JSON error handling to fit similar convention
revise JSONPARSE exception to use original exception object
Merge pull request #29 from mostlygeek/master

Add a try/catch around JSON.parse