Add Start, Stop, Pause, Unpause, Suspend, & Resume

Fixes #190.

These six functions, of which Start and Stop are undocumented on
OpenStack's API reference, should facilitate an easier method to place a
server into a suspended-animation state.

Pausing a server will cease its operation, but will hold its state in
the hypervisor's RAM.  Suspending a server will cease the operation and
write the results to disk or other non-volatile medium.  No idea
what-so-ever what Stop does.  Use Stop at your own risk.
diff --git a/interfaces.go b/interfaces.go
index 4c7dbee..d73f11d 100644
--- a/interfaces.go
+++ b/interfaces.go
@@ -244,4 +244,29 @@
 	// GetSGRule obtains information for a specified security group rule.
 	// This method only works if the provider supports the os-security-groups-default-rules extension.
 	GetSGRule(string) (*SGRule, error)
+
+	// Pause stores the state of the server in RAM.  A paused instance continues to run in a frozen state.
+	Pause(id string) error
+
+	// Unpause restores normal behavior of a previously paused server.
+	Unpause(id string) error
+
+	// Suspend stores the state of the server on disk or other non-volatile medium.
+	// Administrative users might suspend an infrequently used instance or suspend an instance to perform system maintenance.
+	// Suspending an instance is similar to placing a device in hibernation;
+	// memory and vCPUs become available to create other instances.
+	Suspend(id string) error
+
+	// Resume restores normal behavior of a previously suspended server.
+	Resume(id string) error
+
+	// Start restores a previously stopped server to normal operation.
+	// WARNING: This function depends on a Nova action which remains undocumented on the OpenStack API Reference website,
+	// and may be deprecated in favor of Pause/Unpause, or Suspend/Resume.
+	Start(id string) error
+
+	// Stop stops a server.
+	// WARNING: This function depends on a Nova action which remains undocumented on the OpenStack API Reference website,
+	// and may be deprecated in favor of Pause/Unpause, or Suspend/Resume.
+	Stop(id string) error
 }