Add AT parser
Use DateTime object for date in Sms class
Add to_hayes method to some basic classes
Move AT commands in Hayes class and use Modem to send to SerialPort
Add swap files to gitignore
Add tests using Rspec
Remove useless file
Add PDU mode support and GSM 7Bit encoding / decoding
Use Forwardable in Biju::Modem
Add timezone to DateTime format
Remove useless self from to_hayes methods
Modify parser for PDU mode
Add length parameter to GSM7Bit decode
Add tests for GSM7Bit
Add UCS-2 encoding / decoding for SMS user data
Add request before response in parser
Add +CMGF? support and text_mode? method
Disable text mode and generate Sms objects in PDU mode

Text mode is only useful for debug purposes.
To parse answers, PDU mode is required (multiline messages, ...).