faidx reader for golang using biogo's io.seqio.fai
f, err := faidx.New("some.fasta")
check(err)
seq, err := f.Get("chr1", 1234, 4444)
st, err := f.Stats("chr1", 1234, 4444)
// fractions of GC content, CpG content and masked (lower-case)
st.GC, st.CpG, st.Masked