Flowio

* Adds official support for Python 3.11 & 3.12
* Allow creation of FCS files without any events (thanks to tristan-ranff for PR 26)
* MAINTENANCE: moved to a 'src' based directory structure using pyproject.toml
* DOCUMENTATION: moved to RTD doc theme

* BUGFIX: fixes parsing of FCS files with integer data type where bitmasking is needed to properly retrieve event values greater than the PnR value (thanks to JcGKitten for PR 24)
* BUGFIX: fixes issue where file wasn't closed before raising error for multi-dataset FCS files

* Support added for FCS files with multiple data sets (via '$NEXTDATA' tag). Special thanks to Max (JcGKitten) for implementing this feature (23)!

* BUGFIX: Fixed an issue where FCS files were not being closed when an error occurred while parsing the file.
* All errors / exceptions raised in FlowData class are now inherited from the FlowIO generic class `FlowIOException`

* Reduce time to create new FCS files
* Support additional parameter related FCS keywords when creating new FCS files
* Error raised when creating FCS files with non-float data type
* API: Custom exceptions / errors are now thrown. These can be imported via the module flowio.exceptions
* API: FlowData constructor added `ignore_offset_discrepancy` option to ignore discrepancy between the HEADER and TEXT values for the DATA byte offset location
* API: FlowData constructor added `use_header_offsets` option to use the HEADER section for the data offset locations
* BUGFIX: Remove invalid $PnE output for float data type (create_fcs still only supports exporting as float)

Special thanks to zbjornson for PRs 16, 17, 18, 21

BUGFIX: Fixes incorrect data offset for some exported FCS files (issue 14)