only escape Edge#node_one and Edge#node_two when output

Theory#adjancy_matrix, Theory#incidence_matrix, and
Theory#distance_matrix all depend on Edge#node_one and Edge#node_two to
access other nodes in the graph. Because GraphViz#get_node expects an
unescaped node id, but node_one and node_two were escaping, this caused
nil to be returned from GraphViz#get_node calls.

The only place that required escaping for Edge#node_one ad Edge#node_two
was in Edge#output.

So escaping was removed from Edge#node_one and Edge#node_two, but added
to their usage in Edge#output.
Escape reserved words in node IDs
Add the solution, based in check if the node names are valid, this is done at output process of the node and the edge. Since the problem just occurs when outputting, more especially in the generate dot file, with don't accept nodes with certain names. I did this way, so would have less impact in the rest of the code.
Remove some print debugs and comment code that became trash
Merge branch 'josephholsten-push-escaping-into-output'
...
Merge branch 'fix-reserved-words' of https://github.com/joaomsa/Ruby-Graphviz
Merge branch 'node_name_error' of https://github.com/joaozeni/Ruby-Graphviz into joaozeni-node_name_error

Conflicts:
	lib/graphviz/edge.rb
Merge branch 'joaozeni-node_name_error'
Prepare for 1.1.0