Some code restructuring

    Moved hashtag getting and tweeting to functions in
    core.py to be able to reuse them.
Added Command line interface
Merge pull request #1 from cheglastgnat/restructuring

- Moved core methods to new file 'core.py'
- Methods directly relevant to the Twitter scripting bot are held in 'script.py'
- New file 'cli.py' offers a command line interface to some Twitter-related functions (for now: Get list of trending topics for a location)