Update minitest-capybara

Newer minitest-capybara has dropped minitest-matchers dependency.
Instead of generating assertions and expectations from matchers,
assertions and expectations are now defined in minitest-capybara.
This means the assertions are a slightly different name now.
Add Capybara documentation

Make it easier to find the correct assertions and expectations by
documenting them in this project.
Deprecate old assert_have_* methods

Give a deprecation warning when used, but allow then to be called for now.
Update manifest and gemspec
Allow feature to work without "Feature Test"

Capybara::Rails::TestCase matches against "Feature Test", which must
be at the end of the describe string so the spec will be matched.
This can be dropped when using `feature` instead of `describe`.
Call reset_sessions! after tests [closes #7]
Silence deprecation warning in tests
Version bump for 0.10 release