Add command to fire your editor from this tool.

Uses $EDITOR by default. But editor can be configured
by setting an option in the todotxt.cfg called todo_txt_editor.
This is documented in that file.
Add task "edit" to readme.
Merge pull request #3 from berkes/feature/editor

Add command to fire your editor from this tool.
driven out basic config reading and parsingw
Raise error when both old and new config are used
Initial support for multiple files.

This commit adds preliminary support for more then
one file using the --file option.
It defaults to todo.txt, but any amount of files can
be provided in the config file.

Note that this requires a change of setup in the
 config file, which is not backwards compatible!
 hence we set a DEPRECATION warning if old config
 is found.

This is the first step towards more actions, such
as

* "move" to move todos between files,
* "archive" to move done items to done.txt.
* "backup" to move files to a "backup.txt" and so on.

For now, however, one can simply add --file=foo to perform
any todotxt action on that file instead of the default todo.txt.
Cleanup and refactor validation and parsing.
Assert backwards compatibility.

By falling back on todo_txt_path when that is found and no other
todo path is given.
Refactored messaging to send user messags in a bit cleaner way.
Introduce todofile with tests to handle the file-actions.
draft for speccing the cli
Move auto-generate out of init.
removing cli testing. Will be replaced with Aruba soon.
introduce the move command.
refactor initialisation. cleaner and easier to read,
Add coverage report directory to ignores.
add simplecov to list of development gems
Add helper file which initialises simplecov
introduce clihelper spec.

All tests, however, are pending; first the existing code
must be made a tad more testable.
Init takes any number of args, don't force passing "config"