detect project and rails root
Merge pull request #46 from senny/gemfile_traversal

detect project and rails root
fix typos
Tweak error messages and related code

* I found the distinction between "project root" and "application root" a
  bit confusing, so tried to make that clearer.

* Addded a test. The Gemfile one is hard to test because there is a Gemfile
  upstream of the test application (the Gemfile for spring itself).

* Moved Spring.verify_environment! to the Run command so that e.g.
  `spring help` works on its own.
do not crash on missing test name
unify test case superclass to `ActiveSupport::TestCase`.
Merge pull request #47 from senny/do_not_crash_on_missing_test_name

spring test should not crash on missing test name
unify test definition to `test "" do`
Spring commands can define files to preload
Merge pull request #45 from senny/only_require_spec_helper_if_present

configure what files will be preloaded
bump version
document how to modify preloaded files
Editing documentation