v0.31.0

• Huge performance increase for queries! Added sortable index, big refactor #114
• Added store.query() function with better query options, such as starts_at and limit. Under the hood, this powers Collections,
• Resource.save returns a CommitResponse.
• Refactor Commit.apply_opts, structure options.
• Remove the potentially confusing commit.apply method.
• store.tpf now takes a Value instead of String.
• Improved sorting logic. Still has some problems.