## Changes
Before this change maps were stored as a regular Go map with string
keys. This didn't let us capture metadata (location information) for map
keys.
To address this, this change replaces the use of the regular Go map with
a dedicated type for a dynamic map. This type stores the `dyn.Value` for
both the key and the value. It uses a map to still allow O(1) lookups
and redirects those into a slice.
## Tests
* All existing unit tests pass (some with minor modifications due to
interface change).
* Equality assertions with `assert.Equal` no longer worked because the
new `dyn.Mapping` persists the order in which keys are set and is
therefore susceptible to map ordering issues. To fix this, I added a
`dynassert` package that forwards all assertions to `testify/assert` but
intercepts equality for `dyn.Value` arguments.
## Changes
This change adds the following functions:
* `dyn.Get(value, "foo.bar") -> (dyn.Value, error)`
* `dyn.Set(value, "foo.bar", newValue) -> (dyn.Value, error)`
* `dyn.Map(value, "foo.bar", func) -> (dyn.Value, error)`
And equivalent functions that take a previously constructed `dyn.Path`:
* `dyn.GetByPath(value, dyn.Path) -> (dyn.Value, error)`
* `dyn.SetByPath(value, dyn.Path, newValue) -> (dyn.Value, error)`
* `dyn.MapByPath(value, dyn.Path, func) -> (dyn.Value, error)`
Changes made by the "set" and "map" functions are never reflected in the
input argument; they return new `dyn.Value` instances for all nodes in
the path leading up to the changed value.
## Tests
New unit tests cover all critical paths.
Pieter Noordhuis