Update README [ci skip]

Outlines desired design for rewrite/refactor of functionality.
Reorganize test models and migrations

Run migration in `before(:suite)` block. Remove unused code
(`AccountQuery`, including `Paraphrase::Syntax::Relation` into
`ActiveRecord::Relation`).
Refactor query spec using a single Query class

Add `Post` model and `PostQuery` with the minimal features to test
`Query` functionality.
Infer query source from class name or manually specified attribute
Default params to empty hash
Add recursive `params` scrubbing

Cleanup `params` setup and remove call to `#freeze`.
Remove `results`, build `relation` on initialization

Enables `Query` to act as an enumerable proxy to the final query that is
built.
Require 'scope_mapping' in paraphrase.rb
Rename `ScopeMapping` to `Scope`

Replace all references to `mapping(s)` with `scope(s)`.
Update signature of `Query#map` and `Scope#new`

Put query parameters as first arguemnt so `Query#map` reads more
intuitively (mapping query params to scopes, not scopes to query
params).
Determanistically create `method` object in `Scope`

Since `Query` is always initialized with an `ActiveRecord::Relation`,
`Scope` does not need to handle if the `relation` passed to
`Scope#chain` is an `ActiveRecord::Base` subclass.
Refactor `Scope` specs

Add factory method for building scopes. Remove tests for `:require`
option until a proper use case can be determined or the code around this
feature can be simplified.
Add `Query#[]` to read query param values

Allows defining custom readers, otherwise reads from `params`.
Refactor `Scope#chain`

Remove `:require` option until that functionality is driven by a
real-world use-case.
Remove unneeded requires in spec_helper
Convert specs to RSpec 2.14.7 syntax with Transpec

This conversion is done by Transpec 1.7.0 with the following command:
    transpec

* 13 conversions
    from: obj.should
      to: expect(obj).to

* 6 conversions
    from: obj.should_not
      to: expect(obj).not_to

* 4 conversions
    from: obj.should_not_receive(:message)
      to: expect(obj).not_to receive(:message)

* 4 conversions
    from: obj.should_receive(:message)
      to: expect(obj).to receive(:message)
Update Syntax module

Not necessary to add a module for `ActiveRecord::Relation`. The Syntax
module can be included into `ActiveRecord::Relation` to acheive the
previous same functionality. Remove `register_mapping` API in favor of
defining query classes exclicitly as a subclass of `Paraphrase::Query`.
Move models to spec_helper

Easier to manage.
Allow passing a model class or relation to `Query`

Defer to `Scope#chain` to resolve whether `relation` is an
`ActiveRecord::Base` subclass or an `ActiveRecord::Relation`.
Install gems concurrently