Implement Smith-Waterman-Gotoh algorithm

[tdebatty]

"An Improved Algorithm for Matching Biological Sequences", Gotoh (1982):
The algorithm of Waterman et al. (1976) for malchirlg biological seyuences was modified under some limitations to be accomplished in essentially MN steps, instead of the M²N steps necessary in the original algorithm.
http://www.genome.ist.i.kyoto-u.ac.jp/~aln_user/archive/JMB82.pdf