Merge pull request #123 from touzbi/master

Added http status code tests (400, 401, 403)
Merge pull request #124 from touzbi/master

'skipDuplicates' bug  + test case
Update README.md
If queue an undefined value, should skip it
Fix this issue: https://github.com/sylvinus/node-crawler/issues/126
Merge branch 'master' of github.com:sylvinus/node-crawler
0.4.1