Add support for Airgram

Airgram requires a POST over HTTPS, which is not possible with the "url" service so it has been introduced as a service on its own.

README.md

@@ -11,6 +11,7 @@ conditions.  ZNC Push current supports the following services:
 * [Prowl][]
 * [Supertoasty][]
 * [PushBullet][]
+* [Airgram][]
 * Custom URL GET requests
 
 This project is still a Work In Progress, but should be functional enough and stable enough
@@ -212,6 +213,7 @@ to something similar to "http://domain/#channel/2011-03-09 14:25:09", or
     *   "prowl"
     *   "supertoasty"
     *   "pushbullet"
+    *   "airgram"
     *   "url"
 
 *   `username = ""`
@@ -233,7 +235,7 @@ to something similar to "http://domain/#channel/2011-03-09 14:25:09", or
     When using Pushover, this option allows you to specify a single device name to send
     notifications to; if blank or unset, notifications will be sent to all devices.
 
-    This option must be set when using PushBullet.
+    This option must be set when using PushBullet and Airgram.
 
 ### Notifications
 
@@ -414,6 +416,7 @@ This project is licensed under the MIT license.  See the `LICENSE` file for deta
 [Prowl]: http://www.prowlapp.com
 [Supertoasty]: http://www.supertoasty.com
 [PushBullet]: https://www.pushbullet.com/
+[Airgram]: http://airgramapp.com/
 
 [issues]: http://github.com/jreese/znc-push/issues
 [ZNC]: http://en.znc.in "ZNC, an advanced IRC bouncer"

push.cpp

@@ -456,6 +456,20 @@ class CPushMod : public CModule
 					i->second = expand(i->second, replace);
 				}
 			}
+			else if (service == "airgram")
+			{
+				if (options["target"] == "")
+				{
+					PutModule("Error: target (email) not set");
+					return;
+				}
+
+				service_host = "api.airgramapp.com";
+				service_url = "/1/send_as_guest";
+
+				params["email"] = options["target"];
+				params["msg"] = message_content;
+			}
 			else
 			{
 				PutModule("Error: service type not selected");
@@ -1084,6 +1098,10 @@ class CPushMod : public CModule
 						{
 							PutModule("Note: URL requires setting the 'message_uri' option with the full URL");
 						}						
+						else if (value == "airgram")
+						{
+							PutModule("Note: Airgram requires setting the 'target' with the email address of the recipient");
+						}
 						else
 						{
 							PutModule("Error: unknown service name");