Update implementation of jaccard_index

Uses set operators to find intersection and union of given
enumerables

Update implementation of jaccard_index

Uses set operators to find intersection and union of given
enumerables

remove pry
update documentation
namespace chebyshev
namespace cosine and euclidean
namespace remaining modules

including maxmin, minkowski, tanimoto; updates callbacks
for cosine, tanimoto
use instance_eval and class_eval to add functionality within modules
add regression specs for ensuring both include and extend work as expected
add specs for including levenshtein module
Merge 'ability_to_require_family_methods_separately'

Original:

> Merge branch 'ability_to_require_family_methods_separately' of https://github.com/rossta/measurable into rossta-ability_to_require_family_methods_separately