refresh rspec config + update files
Merge pull request #660 from guard/rspec_update

add minor rspec config improvements
improve detecting used plugins [fix 659]

- and fail when accessing contents before reading Guardfile
- the specs are still messy, but this will be fixed in near future
Merge pull request #659 from guard/fix_659_detecting_used_guards

'guard init' keeps appending the same templates to Guardfile
Release 2.7.3
deprecate lib/guard/guard.rb  [fix #647]

- show deprecations by default
- '--show-deprecations' is now useless (updated README)
- disable deprecations for methods Guard uses internally (sic!)