## Changes
This removes the need for the `allowMissingKeyInMap` option to the
private `visit` function and ensures that the body of the visit function
doesn't add or remove values of the configuration it traverses.
This in turn prepares for visiting a path pattern that yields more than
one callback, which doesn't match well with the now-removed option.
## Tests
Unit tests pass and fully cover the inlined code.
## Changes
This change means the callback supplied to `dyn.Foreach` can introspect
the path of the value it is being called for. It also prepares for
allowing visiting path patterns where the exact path is not known
upfront.
## Tests
Unit tests.
## 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