Add MergeIncidents (using Incident)

Allows for merging of incidents as follows:

    incidents := make([]string, 3)
    incidents[0] = "PXXXXXX"
    incidents[1] = "PYYYYYY"
    incidents[2] = "PZZZZZZ"

    first := incidents[0]
    rest := incidents[1:]

    tomerge := make([]pagerduty.APIObject, 0)

    for i := range rest {
	    inc := pagerduty.Incident{
		APIObject: pagerduty.APIObject{
		    ID:   rest[i],
		    Type: "incident_reference",
		},
	    }
	    tomerge = append(tomerge, inc)
    }
    result := client.MergeIncidents(email, first, tomerge)

incident.go

@@ -90,6 +90,17 @@ func (c *Client) ManageIncidents(from string, incidents []Incident) error {
 	return e
 }
 
+// MergeIncidents
+// Uses Incident to match ManageIncidents
+func (c *Client) MergeIncidents(from string, id string, incidents []Incident) error {
+	r := make(map[string][]Incident)
+	r["source_incidents"] = incidents
+	headers := make(map[string]string)
+	headers["From"] = from
+	_, e := c.put("/incidents/" + id + "/merge", r, &headers)
+	return e
+}
+
 // GetIncident shows detailed information about an incident.
 func (c *Client) GetIncident(id string) (*Incident, error) {
 	resp, err := c.get("/incidents/" + id)