adaptive momentum by default, Euclidean is now SqEuclidean (W2), Euclidean is for W1 and uses `jnp.linalg.norm` to ensure differentiability

What's Changed

• default momentum with start=300 by @marcocuturi in #155
• Unbalanced gromov by @LaetitiaPapaxanthos in #128
• Euclidean / SqEuclidean and changes in power by @marcocuturi in #157

Full Changelog: 0.2.10...0.2.11