Summary metadata tag for og:description and fix excessive line length

input/error/400.html

@@ -1,4 +1,5 @@
 [//]: # "Title: Malformed Request"
+[//]: # "Summary: The server received a malformed request."
 
 <div class="err">
     <h1>Malformed Request</h1>

input/error/401.html

@@ -1,4 +1,5 @@
 [//]: # "Title: Client Unauthenticated"
+[//]: # "Summary: Authentication is required to access this resource."
 
 <div class="err">
     <h1>Client Unauthenticated</h1>

input/error/403.html

@@ -1,4 +1,5 @@
 [//]: # "Title: Access unauthorised"
+[//]: # "Summary: Access to this resource has been prohibited."
 
 <div class="err">
     <h1>Access Unauthorised</h1>

input/error/404.html

@@ -1,4 +1,5 @@
 [//]: # "Title: Not Found"
+[//]: # "Summary: The resource requested not found on this server."
 
 <div class="err">
     <h1>Not Found</h1>

input/error/405.html

@@ -1,4 +1,5 @@
 [//]: # "Title: Request Method Disallowed"
+[//]: # "Summary: The request method used for this resource has been disallowed."
 
 <div class="err">
     <h1>Request Method Disallowed</h1>

input/error/502.html

@@ -1,4 +1,5 @@
 [//]: # "Title: Bad Gateway"
+[//]: # "Summary: The upstream resource is unavailable."
 
 <div class="err">             
     <h1>Bad Gateway</h1>

input/error/504.html

@@ -1,4 +1,5 @@
 [//]: # "Title: Gateway Timeout"
+[//]: # "Summary: The upstream resource is unavailable."
 
 <div class="err">             
     <h1>Gateway Timeout</h1>