Synop2bufr

**Bug Fix**
- Fixed bug where the return object lacks the `_meta` key when the station is missing from the metadata.
- The `transform` function is generally more thorough in checking whether the conversion is successful or not before running blocks of code.

**Bug Fixes**
- The return objects now always have the same structue for the `_meta` key, which prevents the bug `Error: '_meta'` when stations can't be found in the metadata or a report can't be parsed. This now means the warning and error messages have been moved to `result["_meta"]["result"]["warnings"]` and `result["_meta"]["result"]["errors"]` respectively.
- Updated `cli.py` to handle `NoneType` objects returned in the `_meta` key correctly so that no CSV file or BUFR file is written for unsuccessfully decoded reports.

**Main Changes**
- Pymetdecoder and csv2bufr logs are now captured and stored appropriately in warning and error arrays which can be accessed in the webapp.
- Valid min and max values have been implemented directly into the 307080 and 307096 mapping files so that out of range errors are handled before ecCodes and are more informative for the user. Many of these valid ranges have been taken from the [WMO Guide to Instruments and Methods](https://library.wmo.int/viewer/41650/?offset=#page=47&viewer=picture&o=bookmark&n=0&q=).
- A verification that, if both reported, the dewpoint temperature is less than or equal to the air temperature has been added.
- Unit tests have been added for the two quality control steps above.
- NIL reports are no longer written as an empty BUFR and the user is informed of this through a warning.
- Test data has been updated, most notably the wis2box-data now has a `barometer_height` column to meet the current requirements of synop2bufr.

**Bug Fixes**
- When `iR = 3`, absent precipitation groups represent zero preciptation, not missing data. Previously this was not supported and precipitation levels were set to missing.
- Section 3 and section 4 mappings were not being updated correctly which caused the incorrect error `Missing station height`.

This release provides improved handling of warnings and errors, as well as support for the wis2box webapp.

This release provides the following updates:

- Dynamic use of the 307080 and 307096 templates depending on the method of wind measurement.
- Encoding of the barometer height obtained from the station list file.
- Support for `nil` reports.
- Support for transformation of multiple GTS messages in one file by partitioning according to the end of message signal `nnnn`.
- A CSV file is output during transformation, containing the decoded data of the input file where each row corresponds to each successfully converted report.
- Restructuring of the example data, addition of Cuban GTS data and synthetic data (which contains almost all possible groups that can be written in a synop report).
- Updated unit tests.
- Various bug fixes found by testing with different GTS data.

Encoding of station height