Enum String Representation

• closes #154: #154
  • enums now return their underlying value when converted using __str__()

Maintenance Release

• closes #153: #153

NMEA Tag Blocks

• closes #150: NMEA tag blocks (thanks to @Leila-Codes)
• adds TagBlockQueue: rudimentary support for NMEA tag block grouping

Fix: Import Error on Windows

• partially reverts #148 to fix an import error on Windows

Quality of life: `close()` for TCP/UDP sockets

• exposes close() for TCP/UDP sockets (@mib1185)

Feature: allow for message preprocessing

• adds the PreprocessorProtocol to support custom message formats
• DROPS support for Python 3.7 (EOL)
• minor correction in the documentation (thanks to @lsamaciel)

Improves the API of `FilterChain`

• improves the API of FilterChain
  • FilterChain.filter(stream) now accepts a stream instance
  • this stream MUST implement the Stream interface defined in pyais.stream
  • individual messages can be filtered using IterMessages(...)

Bug Fixes

• merges #135 (by @prefixFelix)
  • fixed the length of the UTC hour and minute field
• closes #136
  • resolved logic error to accurately distinguish between SOTDMA and ITDMA communication states

Extra Fields for AISTrack

• merges #134 (by @alfonnews)
• adds additional fields to AISTrack

Adds `get_country(mmsi)` to get the code/name of country from MMSI

• closes #131
• pyais now supports country codes/names using get_country(mmsi)