v0.6.3

Fixed

• Error not being raised on alphabet detection failure in SequenceFile or MSAFile.
• Add check in DigitalSequence constructor to make sure encoded characters are in valid range (#25).

Added

• SequenceFile.guess_alphabet and MSAFile.guess_alphabet to guess the alphabet from an open file.
• Alphabet.encode and Alphabet.decode to convert raw sequences between digital and text format.