Do not use ATZ command on initialization

ATZ can reset settings like SMSC number on some 3G keys.
Add generic rule for responses in parser
Add class for PDU 'first octet' field
Clean Biju::PDU.decode method
Flush serialport output before every AT command
Ignore PDU message lines in response when sending SMS

Tested with TP-LINK MA180.
It returns the PDU message when sending a message with a length greater
than 56 (i don't really know why for now). These lines are ignored and
only the last one with the status is parsed.
Allow for an id or an enumerable for Biju::Hayes#delete
Add count on repeat when at least one occurence is required