explicit "information as evidence" concept

#### Definitions
From the Genealogical Proof Standard, this proposal assumes the following definitions:
* *Source* &mdash; an *Information* container
* *Information* &mdash; data extracted of the *Source*
* *Evidence* &mdash; *Information* selected and used to answer a *Question*

In graphical form:
![InformationAsEvidenceDomainConcepts](https://f.cloud.github.com/assets/840078/392605/26b35c66-a782-11e2-9580-2b3dcae4d5d9.png)

#### In the GEDCOM X Model

*Sources* are described with instances of `SourceDescription`.

*Information* can be modeled with instances of `Conclusion` that have `extracted` set to “true”.

We do not explicitly model genealogical *Questions* in GEDCOM X.  Instead, the model allows *Answers* to be captured in instances of `Conclusion`.  The `Conclusion` *type* is maybe the best hint as to what *Question* was being answered.

In the GEDCOM X model, the mechanism for relating __*information*__ with a __*question/answer*__ is an instance of `Identifier` with its `type` set as `http://gedcomx.org/Evidence`.

#### Proposal

We would like concept of __*evidence*__ to be more explicit in the GEDCOM X model&mdash;to make the association between __*information*__ and its __*question/answer*__ its own extensible entity.  We are, therefore, submitting for your review, a proposal to add an `EvidenceReference` entity.

`EvidenceReference` has the following members:
* `resource` &mdash; the representation of *information*
* `attribution` &mdash; attribution for the reference

We propose that an `evidence` member be added to the following top-level specializations of `Conclusion`:
* Person
* Relationship
* Event
* PlaceDescription