Created Leaderboard API (markdown)

Leaderboard-API.md

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+# Transaction Upload API
+
+## `POST /api/stats/leaderboard`
+
+Takes an `application/json` post request.
+
+### Request JSON
+
+```
+{
+  session_key : <current session key>,
+  type : <leaderboard type>,
+}
+```
+
+Where type is one of:
+
+* `daily_total`
+* `daily_count`
+* `weekly_total`
+* `weekly_count`
+* `monthly_total`
+* `monthly_count`
+* `global_total`
+* `global_count`
+
+### Response JSON
+
+#### Success
+
+Response code of `200 OK`
+
+```
+{
+  success : true,
+  leaderboard : [
+    {
+      display_name : <User Display Name>,
+      value : <leaderboard value>,
+      trend : <trend>
+    },
+    ...
+  ],
+  user_position : <Current User Position>
+}
+```
+
+Where trend is:
+
+* `1` : Climbing the Leaderboard
+* `0` : No change in Leaderboard position
+* `-1` : Descending the Leaderboard
+
+And `user_position` is the place of the user in the leaderboard - *zero indexed*!
+
+#### Failure
+
+If something is missing from the request, or is invalid, you will get a response code of `400 BAD REQUEST` and the following:
+
+```
+{
+  success : false,
+  message : <error message>
+  error : <error type>
+}
+```
+
+If there was a server error, you will get a `500 SERVER ERROR` and possibly the following:
+
+```
+{
+  success : false,
+  message : 'An unknown error occurred when adding the transaction'
+  error : 'server_error'
+}
+```
+
+The error messages should describe what was wrong with the submission