added preliminary action 'init' and small fixes
Added flag '--dest,-d' to the init action and improved help for env action
small fixes
Ensure that tasks are always on a single line
Various enhancements for the 'add' command:

- attempt to honor -t|-T global flag (supporto for env var
  TODOTXT_DATE_ON_ADD is not ready);
- display the number of the task;
- use buffered I/O;
- code clean-up;
Improved help description for the 'add' command