Update changelog for v3.0.0. [ci skip]
Release 3.0.0
Don’t create circular ruby gems dependency.

rspec depends on rspec-(core|mocks|expectations), each
of which depends on this gem...so we shouldn’t depend
on rspec in turn from here.

Our gemfile takes care ensuring we have all of RSpec available
when running the specs.
Merge pull request #75 from rspec/remove-rspec-dependency

Don’t create circular ruby gems dependency.
Move the directory maker into RSpec::Support
Use an isolated directory for the DirectoryMaker specs
Add tests for existing file and relativ path
Better docstring for the DirectoryMaker
Add absolute path testing to the DirectoryMaker
Curate specs a little for DirctoryMaker
Remove fileutils require