Hi there,

First thank you for creating this wonderful tool!

One little glitch I noticed is that seqkit subseq --feature is not case insensitive while the docs says that

      --feature strings   select limited feature types (multiple value supported, case ignored, only
                          works with GTF)

To reproduce:
Get GENCODE genome and annotation, e.g., Gencode_mouse/release_M32/GRCm39.primary_assembly.genome.fa.gz and Gencode_mouse/release_M32/gencode.vM32.primary_assembly.annotation.gtf.gz, and run

seqkit subseq \
    --gtf Gencode_mouse/release_M32/gencode.vM32.primary_assembly.annotation.gtf.gz
    --feature CDS \
    Gencode_mouse/release_M32/GRCm39.primary_assembly.genome.fa.gz

will get the expected output but running it with --feature cds will not output anything.

Am I getting the docs wrong or is this an actual little bug,

Cheers