Fix typo in --pomodoro-prefix help string

The --pomodoro-prefix says the default is "B" instead of "P".
Option to send blank output if there's no session

Include --auto-hide to output a blank string if the session file
doesn't exit.
Show break prefix/suffix: print_break_output_hours

The break prefix and suffixes weren't being included in the
print_break_output_hours routine.
Merge pull request #23 from mickboldon/dev

Fix typo in --pomodoro-prefix help string
Merge pull request #24 from mickboldon/autohide

Option to send blank output if there's no session
Merge pull request #25 from mickboldon/fixbsuf

Show break prefix/suffix: print_break_output_hours