Added support for local mode (stdout) and excluding links

[whiskeysierra]

• can now print graphviz code to stdout (to be then passed to dot)
• can now exclude specific link types
• replaced restkit with requests (had issues with query parameter encoding)
• replaced optparse with argparse (to collect multiple excludes)
• added support for epic links
• moved main code into own function to keep namespace clean

[pawelrychlik]

Hi @whiskeysierra, Thanks for the PR, looks very promising! Before I merge, I need to have a closer look & test it - I need a few days, please.

[whiskeysierra]

Just to show how epics would look like: Graph