Catching exception in and_then

[yoavtzelnick]

If an exception is thrown in the function passed to and_then, catch and return error result with the exception message.

Fixes #34

[coveralls]

Coverage decreased (-1.4%) to 98.63% when pulling 7b9064e on yoavtzelnick:bugfix/and_then_catch_exception into 9b64581 on iodevs:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 373d4a1 on yoavtzelnick:bugfix/and_then_catch_exception into 9b64581 on iodevs:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 37e5e3a on yoavtzelnick:bugfix/and_then_catch_exception into 9b64581 on iodevs:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 37e5e3a on yoavtzelnick:bugfix/and_then_catch_exception into 9b64581 on iodevs:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 37e5e3a on yoavtzelnick:bugfix/and_then_catch_exception into 9b64581 on iodevs:master.

[s-m-i-t-a]

Thanks.