Drop ReferenceSetId from SearchReads

This can be inferred from the context of the search, e.g. I search a given set of ReadGroups which are aligned to ReferenceSets, I shouldn't need to specify the ReferenceSet twice.
Merge branch 'master' of https://github.com/ga4gh/schemas into patch-4

Conflicts:
	src/main/resources/avro/readmethods.avdl
Update various Reference{,Set} semantics.
Add pageSize field to all search methods
Constrain the outgoing reference bases alphabet
Add variant sets search method
Merge pull request #133 from calbach/patch-6

Constrain the outgoing reference bases alphabet
Merge pull request #128 from calbach/many-refs

Update various Reference{,Set} semantics.
Merge pull request #123 from cassiedoll/maxresults

Add pageSize field to all search methods
Merge pull request #117 from calbach/patch-4

Drop ReferenceSetId from SearchReads
Update line indents to match style in #111
Merge pull request #139 from cassiedoll/indents

Update line indents to match style in #111
Merge pull request #134 from cassiedoll/variantsets-search

Add variant sets search method