Moves where load path setup and requires happen

* Fixes --require commandline option regression from #831
* Add cucumber documentation for --require
Add changelog entry for --require regression
Improve --require documentation
Deprecate RSpec::Core::Configuration#requires=
Improve --require docs with something more useful

Add deprecation to changelog
Merge pull request #867 from soulcutter/require-option-regression

Require option regression / Deprecate Configuration#requires=