Fastsubtrees

- parallel option for the construction of the tree
- slight performance improvement by validating parents before subtree size calculation

- tree construction: removed performance bottleneck
- tree update/subtree move and reset operations
- CLI: simplified to 'tree', 'attribute' and 'query' commands
- API: aligned to the CLI, by moving code from the commands to the API
- test suite: expanded to complete code coverage
- README: reorganized and made examples with working with tax names and using NtSubtree
- node 0 is now allowed
- subpackage 'ntsubtree' automatically downloads and constructs the NCBI taxonomy tree
- ntsubtree simplifies working with taxonomic names and keeping the data up-to-date
- Github CI Action linting and testing
- documentation is now available at ReadTheDocs

- genomes_attributes_viewer is now a Python package, installable by pip
- separated ntdownload from ntmirror, to ease installation when MariaDB is not available
- updated the documentation
- updated the Docker image/scripts to recent changes

- fix packaging: added missing __init__.py to commands subdir

- single CLI tool with subcommands
- added --tab option to simplify operation with tabular file as input source
- improved the CLI documentation, added examples
- improved the output of the attr query tool

- do not automatically install ntmirror, which is only required for benchmarks
and the example application; this avoids to create a dependency to mariadb
and thus allows simpler installation using pip
- rewrite the Docker image
- tests, benchmarks and example app can be started using a simpler syntax