Reorganization and improvements to hygdrop

This commit includes improvements and reorganization of hygdrop code. It can be summarized as follows

- Plugin architecture implemented. New feature can be added as hy file under plugins directory. And new hy file should contain function `process(connection, event, message)` which is responsible to process message as required. Hygdrop doesn't know what is plugin does processing is delegated to plugin itself.
- Code is now fixed to work with new changes in hy compiler related area
- Spy feature added to bot so it can print python source of input.
- Core member listing for hylang is implemented
- Any project or repo can be given to hy and it will fetch issue/commit for the same from github (previously it was working only for hylang/hy)
- nose test cases added

Some more planned todo's

- [ ] Travis integration
- [ ] pypi integration
- [ ] Fun stuff with bot (more commands in same fashion as fsbot on #emacs)
- [ ] ...