v1.2.0

A release focused on improving developer experience (in preparation for the
upcoming devtools) as well as minor documentation improvements and bug fixes.

• Add metadata to operation context in development (see #305, #324, #325 and #329)
• Fix minor typename memory leak (see #321)
• Fix types for react subscription components (see #328)
• Fix displayName attributes not populated in examples (see #330)
• Fix error in collectTypes method (see #343)
• Fix HTTP status bounds check error (see #348)