Publish a new release

[Morganamilo]

sp-mmr-primitives (substrate/primitives/merkle-mountain-range) can't be released because it has a git dep on ckb-merkle-mountain-range (https://github.com/paritytech/merkle-mountain-range) and the public API has changed since the last release 0.6.0 (10 months ago)

Not releasing sp-mmr-primitives would block the release of the following reverse dependencies:

mmr-gadget (substrate/client/merkle-mountain-range)
mmr-rpc (substrate/client/merkle-mountain-range/rpc)
pallet-mmr (substrate/frame/merkle-mountain-range)
polkadot-service (polkadot/node/service)
rococo-runtime (polkadot/runtime/rococo)
sp-consensus-beefy (substrate/primitives/consensus/beefy)
westend-runtime (polkadot/runtime/westend)

[Morganamilo]

Just realised this is a fork of the crates.io crate. That complicates things slightly.

[Morganamilo]

I've released 0.7.0 from commit 537f0e3 with #4 ontop.