add ComposedSequenceExpressions

[ahwagner]

closes #363

[ahwagner]

Confirmed that ComposedSequenceExpression JSON Schema correctly validates examples:

• Three Repeated Sequence Expressions
• Mixed Expressions
• Nested Composed Sequence Expression (correctly fails)
• Only Literal Sequence Expression components (correctly fails)

But does not correctly validate against this example:

• Single component Composed Sequence Expression

[ahwagner]

331dcfe now correctly validates this example:

• Single component Composed Sequence Expression (correctly fails)

[larrybabb]

@ahwagner great addition. I'm still not fully convinced about how the ordered array is guaranteed. It might be useful to clarify that unless I'm the only one that is missing the technical design behind that.