Adds a simple Repository abstract with some contracts

Adds 3 contracts:

1. `Deleteable`
2. `Insertable`
3. `Updateable`

src/Models/Repositories/Contracts/Deleteable.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace StellarWP\Models\Repositories\Contracts;
+
+use StellarWP\Models\Model;
+
+interface Deleteable {
+	/**
+	 * Inserts a model record.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @param Model $model
+	 *
+	 * @return bool
+	 */
+	public function delete( Model $model ) : bool;
+}

src/Models/Repositories/Contracts/Insertable.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace StellarWP\Models\Repositories\Contracts;
+
+use StellarWP\Models\Model;
+
+interface Insertable {
+	/**
+	 * Inserts a model record.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @param Model $model
+	 *
+	 * @return Model
+	 */
+	public function insert( Model $model ) : Model;
+}

src/Models/Repositories/Contracts/Updateable.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace StellarWP\Models\Repositories\Contracts;
+
+use StellarWP\Models\Model;
+
+interface Updateable {
+	/**
+	 * Inserts a model record.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @param Model $model
+	 *
+	 * @return Model
+	 */
+	public function update( Model $model ) : Model;
+}

src/Models/Repositories/Repository.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace StellarWP\Models\Repositories;
+
+use StellarWP\Models\ModelQueryBuilder;
+
+abstract class Repository {
+	/**
+	 * Prepare a query builder for the repository.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @return ModelQueryBuilder
+	 */
+	abstract function prepareQuery() : ModelQueryBuilder;
+}