Add ScriptableFuture factory method.

Add a factory method, because creating ScriptableFuture in the engine is
repeatedly.

This factory method will be used internally.
Introduce Query API.

This patch only adds interfaces.
Methods will be implemented soon.
Intoduce Schema API.

This patch only adds interfaces.
Methods will be implemented soon.
Introduce Document API.

This patch only adds interfaces.
Methods will be implemented soon.
Introduce Collection API.

This patch only adds interfaces.
Methods will be implemented soon.
Implement Query methods.

This patch implements eq, neq, lt, lte, gt, gte, and and or methods, but
where method is not implemented yet.
See https://github.com/SollmoStudio/beyond/wiki/Beyond-DB-API-Query for
more information.
Implement Schema constructor.

See https://github.com/SollmoStudio/beyond/wiki/Beyond-DB-API-Schema for
more information.
Implement ScriptableDocument constructor.

This constructor is used internally. Users are not allowed to construct
an instance directly. A user must get a ScriptableDocument from
ScriptableCollection.
Implement ScriptableDocument.objectID.

The objectID is read only property that contains Object ID of document.
Implement ScriptableCollection.insert() method.

Insert method receives JavaScript object and returns ScriptableFuture.
Implement ScriptableCollection.find method.

Find method receives ScriptableQuery and returns ScriptableFuture of
Array[ScriptableDocument].
Implement ScriptableCollection.findOne().

FindOne method receives ScriptableQuery and returns ScriptableFuture of
ScriptableDocument. This method returns only the first document unlikely
find method.
Add getter of ScriptableDocument.
Add some of DB API(insert, find and findOne) examples.

This patch adds examples to show how to use DB API.

The number of new examples are three.
 - insert
 - find
 - findOne

To run insert example, send POST to /plugins/insert/{key}/{value}.
This example insert key and value to example.keyValue collection.

To run find example, send POST to /plugins/find/{key1}[/{keyN}]
This example find all documents that the key is one of keyN.

To run findOne example, send POST to /plugins/findOne/{key1}[/{keyN}]
This example find a document that the key is one of keyN.