Improves readablity discussed in issue #38

flow.jison is modified to include a single spaces between vertices and link to improve readablity for issue #38. There should not be any space between vertex and its text and link and its text. flow.spec.js is modified to include three new tests for testing new graphs.  I have created new rules in the flow.jison file with looks like duplicate of previous rule but only contains a additional SPACE terminal symbol for checking single space between vertices and link. If some more modification is required we can discussed them too.