Handle parsing of symbol/icon information

[CBielstein]

Description

Currently, symbols are just kept as the table ID and symbol character on a position. Design a way to move that to some sort of enum or something for the icon being reported. e.g. "Person" or "Jeep" or whatever.

The Position object is probably the correct spot for that information to be encoded and decoded. If that's the case, it may be desirable to remove the public property of table and symbol and just expose the enum. That's up to the implementer and reviewers.

Acceptance Criteria

• Add enum for APRS icons
• Hook up encode/decode logic in the Position class
• Expose on the Position class through a new property
• Consider removing the table and symbol char properties as those are encoding details that most callers won't necessarily care about
• Add tests!

[CBielstein]

Here are the existing enum conversions for comparison. Something like one of these will likely be helpful. https://github.com/CBielstein/APRSsharp/blob/e25bd66e23d1d8f12b1bfabf3fe2569241cac850/src/AprsParser/Extensions/EnumConversionExtensions.cs