Add request source

Add "request" source with support for "method" and "remote-addr"
parameters.  Both values are taken from the raw http.Request object.

Fixes #312

test/hooks.yaml.tmpl

@@ -152,6 +152,15 @@
   include-command-output-in-response: true
   include-command-output-in-response-on-error: true
 
+- id: request-source
+  pass-arguments-to-command:
+  - source: request
+    name: method
+  - source: request
+    name: remote-addr
+  execute-command: '{{ .Hookecho }}'
+  include-command-output-in-response: true
+
 - id: static-params-ok
   execute-command: '{{ .Hookecho }}'
   include-command-output-in-response: true