Make challenge creating function
Merge pull request #13 from shield-9/challenge-func

Enclose challenge creating codes
Use tab to indent instead of space
More readable!
Use single quote

If the string is not using variables in it, I'd like to use single
quote.
Throw Exception
Fix Tests
Update example(PDO)
Add argument type check

More checks will be added soon.
New Exception for user-agent error

This exception is thrown if user-agent passes us error code.
Add autoload.php for non-composer user

This file is originally created by Facebook Team!