Support for Leon compressed fasta/fastq file formats

[Leon](https://github.com/GATB/leon) is a software to compress Next Generation Sequencing data. It can compress Fasta or Fastq format; plain text and gzipped files are supported. In comparative testing, Leon yielded much higher average compression ratios than its peers. Support for these files would be a valuable addition to BioPython, especially for those working with large quantities of fasta/fastq data.

@ianswitzer and I have already brought Leon support to Python via [pyleon](https://jdvne/pyleon) and integration as an optional dependency will require minimal, non-bloating additions to BioPython