Add global before/after instructions to README

I had both `Before` and `After` blocks for my Cucumber tests and required this knowledge in order to use Turnip.

https://github.com/jnicklas/turnip/issues/56
Merge pull request #122 from parkr/patch-2

Add global before/after instructions to README
Change of document formatter specifiers that have been deleted
Use `skip` semantics from `pending` at version greater than 2.99
Overwrite only `Pending` location has been determined before running
Merge pull request #123 from gongo/runnable_rspec_299_and_30

Successful test on RSpec 3.0
Add notes to README about rspec-rails v3.x. #124
Merge pull request #125 from a-suenami/add-notes-for-rails-rspec3

Add notes to README about rspec-rails v3.x.
Replace to CodeClimate badge that shows score
Merge pull request #127 from jnicklas/replace_new_codeclimate_badge

Replace to new CodeClimate badge that shows score
[TWEAK] In one place let(:builder) and let(:feature)
[TWEAK] Add specs about Turnip::Builder::Step
Add `keyword` property of Turnio::Builder::Step
Merge pull request #129 from jnicklas/add_step_keyword

Implemented step `keyword` property
substitute doc string in scenario outline