Status command list application in all terminals

Fixes #93
Test exit status of `spring rspec`

If the specs fail, then the command should have a non-zero exit status.
Correct exit status for `rspec` and `cucumber` commands

Tests from the previous commit now pass. For reference, see the documentation of
RSpec::Core::Runner#run and the code of the cucumber executable.

We probably should put this logic into the fork block of Application#serve. But
unfortunately the different return values for Command#call makes this
impossible.
Merge pull request #105 from geigerzaehler/master

Status command lists applications across all terminals
Replace "spring [console|runner|generate]" with "spring rails"

Closes #76
Rename "spring test" to "spring testunit".

It's longer but it doesn't conflict with the bash builtin "test"
command.

The recommended way to run spring is via binstubs, so people can just
type "bin/testu<Tab>" anyway.

Also, rails 4 will have a "rails test" command that will be integrated
into spring too.

Fixes #64.
Add link to direnv
Add a changelog
bump version
Comment unusual usage of return value

Exiting with an error when a function returns true is counterintuitive. But in
fact Cucumber's `Main::execute` returns false if everything ran cleanly and true
otherwise. So it actually looks more like `failed?`. For reference see
bin/cucumber:14.
Merge pull request #107 from geigerzaehler/rspec_exit

Correct exit status for `rspec` and `cucumber` commands
Fix serialization of client environment.
Merge pull request #110 from oggy/fix-rails-env

Fix serialization of client environment.
refactor mechanism for testing running of 'spring test'

This will help with the next commits.
make "spring test" support multiple arguments

"spring test" needs to accept multiple arguments if guard-minitest is
to ever have a chance of supporting spring.
make "spring test" run all unit tests when given no arguments

With no arguments, it now defaults to running all test-unit tests it
can find, i.e. files matching test/**/*_test.rb.  This is more useful
and arguably more intuitive too.

We need to remove test/performance/browsing_test.rb from the Rails app
being tested, otherwise "spring test" attempts to run this when it
iterates over test/**/*_test.rb, causing a failure due to ruby-prof
not being installed.