Overhaul code to allow asynchronous tweet collection

Allow async tweet collection to finalize the Pyckaxe class. It now does
not need to rely on keyboard interrupts to exit. To do this I also had
to thread the databasehandler as sqlite3 databases cannot be used in
threads in which they are not created (running async runs collection in
a thread).

So basically, we needed a DIFFERENT thread to create and manage the
database.
Heavy refactoring of parsing scripts

Refactoring of a LOT of code so that it fits with the new setup.
Parsing/graphing scripts are now usable as objects or simply standalone
scripts. Rewrite the README file to document changes and how to use the
new stuff.
Merge pull request #8 from dbernard/dont-rely-on-keyboard-interrupt

Dont rely on keyboard interrupt