what remains to be fixed is if it is wrapped
in a `MetricManifold`, or a `ConnectionManifold`, for instance.
In that case, the wrong `translate_diff` methods are called.

A vanilla group has no adjoint_action defined

`translate_diff` is now always computed from adjoint_action instead

adjoint action was previously not available
since not all translate_diff methods were implemented

implement for LeftAction direction, the other direction
is automatic

this ensures that all group methods are now defined

This is the `exp` and `log` associated to any of the
Cartan–Schouten connections. It uses the left-invariant
storage of tangent vectors and the specific exp_lie/log_lie
implementations.

These implementations are the one from *group product*,
so they are not invariant with respect to the semidirect
product.

One could put them back in the product_group layer instead.
The proper way to invoke them is then `exp(base_manifold(G), ...)`
instead of `exp(G, ...)`.

Until this is fixed, `exp` now uses more allocations, even
when calling it with `base_manifold`.

The failing tests come from using matrices instead
of `ArrayPartition`. Using the `ArrayPartition`
type (the one returned by `identity_element`)
works normally.

The invariant log fails when points are too far apart.

more adjoint action methods for CircleGroup

- at Identity
- remove some unused adjoint_action! implementations

…ds.jl into mbaran/lightfolds

…inomial SPD

…variant storage