New configuration option to always record examples.

In current project I'm working on, I've stumbled into the problem not being able to start examples/params recording from `spec_helper.rb`. I want my examples to be always up-to-date without the burden of remembering to run tests with `APIPIE_RECORD` env.

This PR adds method `Apipie.record` which can be used in `spec_helper.rb` or `test_helper.rb` to start examples recording without using `APIPIE_RECORD` env.