sped up base implementation of find_kmems using bidirectional fm-index
sped up base implementation of find_kmems using bidirectional fm-index

[git-p4: depot-paths = "//sw/gpgpu/nvbio/main/": change = 18319554]

NVlabs/nvbio,kimrutherford/nvbio,NVlabs/nvbio,NVlabs/nvbio,kimrutherford/nvbio,kimrutherford/nvbio,NVlabs/nvbio,kimrutherford/nvbio