Minor: Removes debug print statement

Closes: #76

Minor Bugfix Release

Closes the following issues:

• #70
  • The fillbits field was set to fillbits value for every fragment, instead of only the last one. The fillbits field for every other fragment should be set to 0.
• #73
  • when converting ROT values the product was rounded before squaring which led to slightly off ROT values

SOTDMA/ITDMA communication state information

• Closes #17
  • decoded radio state fields
  • provided functions to access SOTDMA/ITDMA communication state information

Bugfixes

Merge pull request #67 from M0r13n/type-27-messages-should-be-signed

Makes type 27 messages lat and lon signed

Removes inconsistencies

• Closes #63 (comment)
  • unifies naming of fields across all message types
  • makes all single bit fields booleans
  • replaces the raw turn value with the actual rate of turn: (turn/4.733)**2
  • makes all data fields raw bytes instead of (large) integers for interoperability
  • makes speed and course floats instead of ints
  • enforces strict types and fixes typing inconsistencies

Bugfixes and improvements

• Closes #54

  • for some fields like speed, lat or lon their types were not properly
    enforced. This led to typing errors and wrong values, e.g. 0 instead
    of 0.0.

• Closes #59

  • when encoding messages the underlying method int_to_bin incorrectly
    assumed that all values were signed. This was wrong and could lead to
    invalid messages, when encoding.

• Closes #58

  • A missing checksum caused a ValueError, which is now ignored

Bug fix: Rename shipname to name for type 21

See #52

Release version 2.0.0

• WARNING: The v2 release will introduce breaking changes
• Introduces the possibility to encode messages
• decoding has been rewritten and implements an iterative decoding approach
• The following fields were renamed:
  • message_fragments -> frag_cnt
  • fragment_number -> frag_num
  • message_id -> seq_id
  • type -> msg_type
  • shiptype -> ship_type
• msg.decode() does not return a pyais.messages.AISMessage instance anymore
  • instead an instance of pyais.messages.MessageTypeX is returned, where X is the type of the message (1-27)
• in v1 you called decoded.content to get the decoded message as a dictionary - this is now decoded.asdict()

Add bounds check for variable length messages

• Correctly handles variable length messages (#40)
  • prior versions were missing required length checks
  • therefore some messages were not correctly decoded
  • this affects Type 7, 15, 16, 20, 22, 24, 25 and 26

Better error messages for `decode_msg`

v1.6.2

Raise a meaningful exception if 'decode_msg' is used improperly (#38)