Add support for Ensemble Fasta format, used by Muscle5

[~j.abbott@dundee.ac.uk] has pointed out that Muscle5 is using a variation of Fasta format to store multiple alignments, each in Fasta format, but in one file.
It adds a single header line to each alignment (in normal Fasta format) starting with "<" followed by a label for the alignment.
An official description can be found at
https://drive5.com/muscle5/manual/efa_file_format.html