gapFind is implemented, gapFill is in tests
Merge branch 'master' into marta-branch

include new features from the master branch, in particular detect_biomass_reaction()
Merge https://github.com/cdanielmachado/framed into marta-branch

GapFill works and the tests are written
include gap Find/Fill + lazy loading on glpk_wrapper + tests
Merge https://github.com/cdanielmachado/framed into marta-branch
bugs due to lazy loading on glpk and different results than gurobi fixed
Merge https://github.com/cdanielmachado/framed into marta-branch
tolerance related fixes

the tolerances in gapFill, gapFind, and blocked_reactions were changed
to 1e-5.
these are needed when integer variables actually have values slightly
different than what's being tested for
glpk_wrapper_lazy added + instructions for python-glpk install updated

instructions to install python-glpk on centOS were included
changed the filename of the glpk_wrapper_lazy
Merge pull request #14 from cdanielmachado/marta-branch

Marta branch