[Feature] Show warning if there are characters not in the FASTA specification #2
Description
Is your feature request related to a problem?
Right now warnings are only shown when calling complement (FastaSequence and LetterCode), at_gc_ratio or gc_content (FastaSequence) methods.
No warning is shown when a sequence has characters not defined in the FASTA specification.
Describe the solution you'd like
It might make sense to show a warning if a sequence has at least a single character not defined in the FASTA specification.