Accept prompt in parser
Return length in encode method for gsm7bit and ucs2
Move PDU fields methods into their own classes
Move GSM7Bit and UCS2 into Biju::PDU::Encoding submodule
Add spec for new PDU classes
Add minimum length for Modem#wait
Improve Hayes#send to check for prompt and wait for answer
Raise a CmsError or CmeError when AT responds with error
Remove mutation of argument string
Add timestamp class to convert from PDU format to DateTime
Remove support for string datetime in SMS
Modify Hayes#messages to always return an array
Add support for +CNUM to get SIM phone numbers
Add timeout to raise exception when Modem#wait is stuck
Add support for +CPIN? and use SIM status before entering PIN