Added pomodoro functionality

It actually works this time!
Update README.md
Improved help and command not recognised messages

They now use format strings so if the commands are changed, they
auto-update
Extracted writing to file as a method
Started adding configurability

Main loop still doesn't handle this, so it is broken.
More progress with configurability
Clean up and bugfix
Major update

Added ability to add, remove, and view timers, along with a major
re-architecturing to simplify the main loop.
Timers now written to config file
Updated todo