analyzedir command

[osma]

The analyze command only analyzes one document. For some backends the startup overhead is very significant so this is inefficient.

We could have an analyzedir CLI command that works similar to evaldir (and MauiTopicIndexer), i.e. it runs analyze on a directory of .txt files and writes the result into TSV files. The file extension / suffix could default to .annif but it should be possible to set on the command line. Something like

annif analyzedir [--suffix .annif] [--limit 10] [--threshold 0.00] [--verbosity INFO] <backend> <directory>

(also --backend-param should be supported)