Better confirmation prompt
Bugfix (task descriptions, newlines)

Fix bug where change of a task's description would add a newline,
without a way to revert it due to how comparison of tasks works.

I am not happy with this fix, but it gets the job done. Maybe it's even
a feature that we are sloppy about trailing whitespace.
Improvements to readme
Rewrite of file format

More todo.txt-like
Add support for custom arguments for editor
Update readme for new format.
More todo.txt-ishnes
Change CLI interface, allow filtering by calendar
Add shortcuts for NEEDS-ACTION and IN-PROCESS
Removed obsolete parts from README