Fixed export
Changes build system to grunt (http://gruntjs.com/).

Most important changes:

- Closure library and compiler have to be downloaded manually now.
- Creates different builds now (minimal, drawing, node and complete) and
  allows custom builds.
- Runs test cases in a headless browser.
Ignores test files.
Removes __iterator__ from graph classes to fix #5.

Since Firefox implements iterators natively and also recognizes them in
'for...in', the property 'Graph.prototype.__iterator__' causes problems in FF.

Removing it was the easiest solution. That means that graph objects cannot be
directly passed to 'goog.iter' methods, but the 'jsnx.helper' methods have been
updated to handle graph objects separately and through that, they work the
same as if they are still iterables.

An iterator can always be created by passing a graph object to
'jsnx.helper.iter'.
Sorts the result and the expected result.

The modified test failed in Firefox because it traverses the nodes in a
different order.
Adds type checking and other verbose options to the compiler.
Fixes most of the new compiler warnings.
Adds "how to use" section to readme.
Implements 'generators/social'.

Adds the following methods:

- jsnx.generators.social.karate_club_graph (jsnx.karate_club_graph)
- jsnx.generators.social.davis_southern_women_graph
  (jsnx.davis_southern_women_graph)
- jsnx.generators.social.florentine_families_graph
  (jsnx.florentine_families_graph)
Implements several methods in 'generators/classic'.

Adds the following methods:

- jsnx.generators.classic.full_rary_tree (jsnx.full_rary_tree)
- jsnx.generators.classic.balanced_tree (jsnx.balanced_tree)

Also fixes a problem with the internal
jsnx.generators.classic.tree_edges_ method when the number of nodes is
0.
Implements 'algorithms/dag'.

Adds the following methods:

- jsnx.algorithms.dag.is_directed_acyclic_graph
  (jsnx.is_directed_acyclic_graph)
- jsnx.algorithms.dag.topological_sort (jsnx.topological_sort)
- jsnx.algorithms.dag.topological_sort_recursive
  (jsnx.topological_sort_recursive)
- jsnx.algorithms.dag.is_aperiodic (jsnx.is_aperiodic)

Further new or changed methods:

- jsnx.helper.gcd (internal): Computes the gcd of two numbers
- jsnx.helper.len now returns the number of nodes when a graph is passed
  (calls G.number_of_nodes internally)
Fix JSHint warnings
Updated compiled files
Updated readme