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)

FIX: inconsistent rounding behavior for ROT

• fixes inconsistent rounding behavior for ROT values
• #130

Fix: logic bug in `NoneFilter`

• fixes a logic bug in NoneFilter
• #128

Filters

• Initial release of the AIS Filters system.
• Basic filtering classes: NoneFilter, MessageTypeFilter, and DistanceFilter.
• FilterChain class to combine multiple filters into a sequence.
• Utility functions haversine and is_in_grid for distance and grid calculations.