Issue #52: Add missing documentation for errors.

help/problem-instances-bad-request.html

@@ -1 +1,3 @@
-<h2>Documentation missing.</h2>
+<h2>Malformed syntax.</h2>
+  <p>The request could not be understood by the server due to malformed syntax.
+  </p>

help/problem-instances-flood.html

@@ -1 +1,3 @@
-<h2>Documentation missing.</h2>
+<h2>Rate limit exceeded.</h2>
+  <p>The user has sent too many requests in a given amount of time. Intended for
+    use with rate limiting schemes.</p>

help/problem-instances-forbidden.html

@@ -1 +1,4 @@
-<h2>Documentation missing.</h2>
+<h2>Forbidden resource access.</h2>
+  <p>The request was a valid request, but the server is refusing to respond to
+    it. Unlike a 401 Unauthorized response, authenticating will make no
+    difference.</p>

help/problem-instances-gone.html

@@ -1 +1,8 @@
-<h2>Documentation missing.</h2>
+<h2>Resource no longer available.</h2>
+  <p>Indicates that the resource requested is no longer available and will not
+    be available again. This should be used when a resource has been
+    intentionally removed and the resource should be purged. Upon receiving a
+    410 status code, the client should not request the resource again in the
+    future. Clients such as search engines should remove the resource from their
+    indices. Most use cases do not require clients and search engines to purge
+    the resource, and a "404 Not Found" may be used instead.</p>

help/problem-instances-not-found.html

@@ -1 +1,3 @@
-<h2>Documentation missing.</h2>
+<h2>Document not found.</h2>
+  <p>The requested resource could not be found but may be available again in the
+    future. Subsequent requests by the client are permissible.</p>

help/problem-instances-service-unavailable.html

@@ -1 +1,3 @@
-<h2>Documentation missing.</h2>
+<h2>Server is unavailable.</h2>
+  <p>The server is currently unavailable (because it is overloaded or down for
+    maintenance). Generally, this is a temporary state.</p>

help/problem-instances-unauthorized.html

@@ -1 +1,6 @@
-<h2>Documentation missing.</h2>
+<h2>Authentication needed.</h2>
+  <p>Similar to 403 Forbidden, but specifically for use when authentication is
+    required and has failed or has not yet been provided. The response must
+    include a WWW-Authenticate header field containing a challenge applicable to
+    the requested resource. See the authentication methods documentation for
+    more information.</p>

help/problem-instances-unprocessable-entity.html

@@ -1 +1,3 @@
-<h2>Documentation missing.</h2>
+<h2>Semantic error.</h2>
+  <p>The request was well-formed but was unable to be followed due to semantic
+    errors.</p>

help/problem-instances-unsupported-media-type.html

@@ -1 +1,4 @@
-<h2>Documentation missing.</h2>
+<h2>Type not supported by the server.</h2>
+  <p>The request entity has a media type which the server or resource does not
+    support. For example, the client uploads an image as image/svg+xml, but the
+    server requires that images use a different format.</p>