MData2 ingest needs to support number format and co-ordinate reference variants

[Scottapotamas]

MData2 packets have two-byte message ID's, where the last byte is used to describe the number format (#7) and coordinate reference (#5).

The ability to generate a correct MID exists for output as part of #9, but adding unit tests for parsing the resulting data fails as the MData2 parser assumes a table which maps to 0xabc0.

• [x] MData2 user-facing event types (XsensEventDataType_t) needs to support fixed-point and double typed data, and the array variations.
• [x] User-facing event union XsensEventData_t needs to support fixed-point and double types
• [x] xsens_mdata2_decode_field() needs to work out the data-type and coordinate frame from the last nibble of the inbound ID
• [x] Find the type in the table without the last nibble applied
• [x] Payload-into-union handling supports additional type possibilities
• [x] Refactor event handling structure to support co-ordinate reference metadata (enum for ENU, NED, NWU etc)
• [x] Existing test cases pass
• [x] Generate test packets with varied data types
• [x] Test case for each type (single, fixed-points, double) rotation matrix outputs
• [x] Write new test cases which include conversion of fixed-point data back to floating point

[Scottapotamas]

This issue is blocked until #11 is resolved.