Build System: Enable python3 compatibility.

* Consistently use spaces in rest-api-templates/asterisk_processor.py.
* Exclude third-party from docs/full-en_US.xml.
* Add docs/full-en_US.xml to .gitignore.
* Use list() to convert python3 view.
* Use python3 print function.
* Replace cmp() with equivalent equation.
* Replace reference to out of scope subtype variable with name
  parameter.
* Use unescaping triple bracket notation in mustache templates where
  needed.  This causes behavior of Python2 to be maintained when using
  Python3.
* Fix references to has_websocket / is_websocket in
  res_ari_resource.c.mustache.
* Update calculation of has_websocket to use any().
* Use unicode mode for writing output file in transform.py.
* Replace 'from swagger_model import *' with explicit import of required
  symbols.

I have not tested spandspflow2pcap.py or voicemailpwcheck.py, only the
print syntax has been fixed.

Change-Id: If5c5b556a2800d41a3e2cfef080ac2e151178c33

rest-api-templates/res_ari_resource.c.mustache

@@ -55,7 +55,7 @@
 #if defined(AST_DEVMODE)
 #include "ari/ari_model_validators.h"
 #endif
-{{^has_websocket}}
+{{#has_websocket}}
 {{! Only include http_websocket if necessary. Otherwise we'll do a lot of
  *  unnecessary optional_api intialization, which makes optional_api harder
  *  to debug
@@ -278,7 +278,7 @@ static int load_module(void)
 
 {{#apis}}
 {{#operations}}
-{{#has_websocket}}
+{{#is_websocket}}
 	struct ast_websocket_protocol *protocol;
 
 	if (ast_ari_websocket_{{c_name}}_{{c_nickname}}_init() == -1) {
@@ -300,8 +300,6 @@ static int load_module(void)
 	}
 	protocol->session_attempted = ast_ari_{{c_name}}_{{c_nickname}}_ws_attempted_cb;
 	protocol->session_established = ast_ari_{{c_name}}_{{c_nickname}}_ws_established_cb;
-{{/has_websocket}}
-{{#is_websocket}}
 	res |= ast_websocket_server_add_protocol2({{full_name}}.ws_server, protocol);
 {{/is_websocket}}
 {{/operations}}