Add missing tests for `set_session`
Fix `set_session.to(nil)` to no longer be a no-op
FilterParamMatcher supports Regexps
Using RSpec 3 for development.
Allow delegate_method to be required independently

This allows the use of the delegate matcher without active support,
fix for issue #561.

* Change `blank?` to `to_s.empty?`
Get validates_uniqueness_of to work better with `NOT NULL` columns

Instead of having to persist the subject, like so:

  describe 'validations' do
    subject { build(:model) }
    it { validates_presence_of :required_attr }
    context "persisted" do
      # Needs to be persisted to prevent NOT NULL db error
      subject { create(:model) }
      it { validates_uniqueness_of :unique_attr }
    end
  end

You can now just write:

  describe 'validations' do
    subject { build(:model) }
    it { validates_presence_of :required_attr }
    it { validates_uniqueness_of :unique_attr }
  end

When required the matcher saves the record to the database.
Updated docs for `ValidateUniquenessOfMatcher` [ci skip]
Tweak validate_uniqueness_of docs [ci skip]
Tweak this test so it's easier to read
Tweak warning to be descriptive, not prescriptive

While we do advise against using the validates_inclusion_of or
validates_format_of validations with boolean columns, we won't judge
if you would like to do so.
validate_absence_of: cast `@attribute` to String

ActiveRecord.columns_hash returns Hash with String keys.
This is why `it { expect(offer).to validate_absence_of(:expired_at) }`
is not working.
Create the define_enum_for matcher
Typo fix in ensure_length_of documentation

Fixing incorrect method name in documentation.
Updated accept_nested_attributes_for_matcher docs [ci skip] 

The matcher is in singular (accept_nested_attributes_for). But the AR class method have to be in plural (accepts_nested_attributes_for)
Add documentation, news for define_enum_for
Rename DelegateMatcher to DelegateMethodMatcher

Matcher classes are named after the matcher method itself.
Fix erratum in docs for delegate_method
Reword failure message for #delegate_method

Currently it says something like this:

    Expected Person#name to delegate to Person#company as #company_name

However, this isn't in line with proper terminology. It doesn't make
sense to say that one method delegates to another; you delegate a method
to another object. So now it says:

    Expected Person to delegate #name to #company object as #company_name

Additionally, we now clarify that #company (in this example) -- or
rather the object returned by #company -- is the delegate object, and if
this object never receives any method calls we say so. Instead of this:

    Calls on Person#company: ...

we say:

    Method calls sent to Person#company: ...

Furthermore, the description (which is shown as the tests are run) was
not correct when `delegate_method` was used against a class rather than
an instance. As an example, the following code:

    it { expect(Person).to delegate_method(:name).to(:company) }

would print out as

    should delegate #name to #company object

and now it prints out as

    should delegate .name to .company object
Move deprecations first, before bug fixes etc.
Bump version to 2.7.0