Closes #70

When delivering a received DLR, the dlr_level parameter were set with
the originally requested value, which is not a correct behaviour.

Fixed so its value is set to the level of the received DLR:

 - dlr_level = 1: means the receipt is coming from the SMSC
 - dlr_level = 2: means the receipt is coming from terminal
Fixes #70

Regex parsing of deliver_sm fixed in order to tolerate flexible DLR
formats from different vendors.

Tests were added to cover clickatell's format (thanks to Ivan Pereira).
Release update from 0.5.3 to 0.5.4
Adding more waiting time to pass travis-ci builds

travis-ci builds are very slow, this will cause tests relying on time to
fail
Fixed tests
Merge pull request #73 from fourat/v0.5-beta

V0.5 beta