Fix lint issue

Add parsing of time and duration and include them in richdata type

Add dgo.Duration type

Adds `dgo.Duration` as a `dgo.Value` representation of `time.Duration`.

Add dgo.Duration type

Adds `dgo.Duration` as a `dgo.Value` representation of `time.Duration`.

Fix assignment to addressable pointers that are nil

When reflecting to a pointer that is unset but addressable, such as a
field in a struct or an entry in a vector, a zero value must be created
before it is filled with data.

Closes lyraproj/hiera#82

Fix pointer confusion when assigning map to struct

The Map was not able to `ReflectTo()` a reflect.Value with kind `Struct`
sinc it assumed that all structs would be sent as pointers. That isn't
the case when the call comes from `FromValue()`.

Let String.String() return string verbatim

Ensure 100% test coverage

Remove use of build tag for test code

Refactor handling of Min() and Max() to common type

This commit adds a sizeRange struct with two uint32 integers for min
and max. This struct implements a common interface used for all types
that have size boundaries.