DSL: Span Queries

[Douglasdc3]

Still a few Query DSL parts missing in this package.

Using https://www.elastic.co/guide/en/elasticsearch/reference/current/span-queries.html
implement the following queries

• Span containing
• Span field masking
• Span first
• Span multi-term
• Span near
• Span not
• Span or
• Span term
• Span within