Give more time to functional test

* Incrementing a test file every second may be too tight for some
* machines.  Change this to 2 seconds.
Add support for multiple directories.

* Initial stab at multiple directory support.  User specifies multiple
* directories via -d command-line option, with each dir separated by
* a comma.
* Change Watcher to use MultiListener.
Add spec for multiple dirs
add --passive option for backgrounding
add option to specify default termination signal

unfortunately, the documentation is potentially confusing, as the
required parameter is not, for example, "SIGTERM" but just "TERM"
Merge pull request #28 from FND/custom-signal

add option to specify default termination signal
Merge remote-tracking branch 'upstream/master' into passive_mode
fixed missing signal parameter
Merge branch 'custom-signal' of https://github.com/FND/rerun
add rb-fsevent to Gemfile, to satisfy Listen on OSX
Merge remote-tracking branch 'upstream/master' into passive_mode
Merge pull request #25 from FND/passive_mode

add --passive option for backgrounding
rename --passive to --background
bump version
extract Options class
--no-growl option
Merge branch 'multidir' of https://github.com/bsia/rerun

Conflicts:
	bin/rerun
clarify docs and tests for multiple dirs
improve readme
improve readme