Simpleais

What's Changed
* Support input from serial sources on Windows by astuder in https://github.com/wpietri/simpleais/pull/4
* fix lon/lat in msg type 27, possibly now also works in types 17 and 22 by astuder in https://github.com/wpietri/simpleais/pull/5
* Adding support for checksum status in stats
*
New Contributors
* astuder made their first contribution in https://github.com/wpietri/simpleais/pull/4

**Full Changelog**: https://github.com/wpietri/simpleais/compare/v0.7.1...v0.7.2

AIS is meant for maintaining a real-time display, so that you don't hit other ships. That means for other uses, there's a lot of pretty-much-redundant information. This library now includes the `aisrefine` tool, which will take a large file and perform lossy compression. At a minimum you'll see one AIS sentence every four hours from a sender, and more if the ship significantly changes things like speed, destination, course, or draught. This provides circa 96% compression on large files, and was a much easier way to speed up the library than rewriting everything in C.

Release available on PYPI: https://pypi.org/project/simpleais/

To make it easier to interoperate with other languages, there is now the ais2json commmand-line tool and support in the Sentence object for converting sentences to JSON. Field order is preserved to make the JSON human-readable. So that no information is accidentally lost, the original encoded AIS text is attached.

The JSON format is much more verbose, but that can be compensated for via compression. A quick test on a 2 GB raw AIS file shows that raw AIS is about 79 bytes per sentence, while a gzipped JSON version is about 64 bytes per sentence.

So that sentences can be easily encoded as, e.g., JSON, they can now be converted to dicts.

This lets you filter AIS packets by timestamp; `aisgrep` now has `--before` and `--after` options. Date format can be anything accepted by the `dateutil` package, which is almost anything.

Contains a variety of improvements, including transparent reading of .gz files, defaulting to quietly ignoring bad lines, and significant speed improvements.