Note proposed Poplin<->PSM APIs

As sent recently by Dave Hill:

  From: Dave Hill
  Subject: Prioritized list of APIs
  To: Karl Fogel
  CC: Trish Heiman, Jeff Cook, Pace Ricciardelli
  Date: Fri, 12 Jan 2018 00:09:17 +0000
  Message-ID: <5212f257efd64f1c9678b75903335f41@EXCH10V.level1a.local>

docs/Poplin-API-proposals.md

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+Proposed PSM APIs for coordinating with the [Poplin project](http://ProjectPoplin.org/).
+========================================================================================
+
+Phase 1
+-------
+
+Most user needs will be met with the ability to access Provider Detail information. 
+
+* **Provider Detail**
+  *Example APIs:*
+    - Get a list of screened providers
+    - Get of list of ineligible providers
+    - Get providers by eligibility date
+    - Update provider address
+    - Update provider contact person
+    - Add provider
+    - Delete provider
+
+Phase 2
+-------
+
+Administrative capability to access more detailed information about the provider’s eligibility lifecycle.
+
+* **Eligibility Determination**
+  *Example APIs:*
+    - Check status of Eligibility Determination
+    - Get Eligibility Determination
+    - Update Eligibility Determination
+    - Delete Eligibility Determination
+
+* **Enrollment**
+  *Example APIs:*
+    - Get Current Enrollments
+    - Get Historical Enrollments
+    - Update Enrollments
+    - Delete Enrollments
+
+Phase 3
+-------
+
+Advanced administrative capabilities.
+
+* **Appeal**
+  *Example APIs:*
+    - Get Current Appeals
+    - Get Historical Appeals
+    - Update Appeals
+    - Delete Appeals
+
+* **Audit**
+  *Example APIs:*
+    - Get Audit
+    - Get actions taken per user
+    - Get actions taken per time period
+    - Get actions taken per provider
+
+* **Messages (Provider Communications)**
+  *Example APIs:*
+    - Get Messages
+    - Get Messages per user
+    - Get Messages per time period
+    - Get Messages per provider