Added basic temporary evidence schema, model methods to get/put/delete it.
added a bit of documentation.
use 'path' prop of req.files file instead of 'filename'.
Added view and route allowing issuers to give badges w/ evidence.
Removing a claim code also destroys any evidence associated with it.
When showing existing codes, list number of temporary evidence items.
Merge branch 'v2.0' into issue-122-evidence-uploading

Conflicts:
	routes/index.js
Report number of evidence items and reserved-for email at /v2/unclaimed.
Added docs for GET/DELETE `/v2/claim/evidence`.
Implemented GET /v2/claim/evidence API endpoint.
Merge branch 'v2.0' into issue-122-evidence-uploading

Conflicts:
	docs/api.md
added s3 health check.
Documented AWS/fakeS3 env vars in README.md.

Also added default fake s3 storage dir to .gitignore.
Redeeming a claim code now destroys any evidence associated with it.
Changed GET /v2/claim/evidence to GET /v2/unclaimed/evidence.

Also removed DELETE `/v2/claim/evidene` from the API docs, since we're
now destroying temporary evidence upon redemption of claim codes.
Webhook now notifies client of evidence items.
merging atuls evidence feature