Implemented stxxl sorting.
Added some ignored pattern to .gitignore.
lsg now produces the overlap graph analyzing only one BWT (new algorithm).
Added operator<< for GSAEntry
Modified bgsa to actually compute the complemented GSA.
Fixed bgsa argument parsing
STXXL is not default anymore (further developments will include STXXL)
Merge branch 'master' of github.com:AlgoLab/LightStringGraph