Create a variation of HelloSignException to denote 404s

[cmpaul]

Per @mveitas:

It would be nice to introduce a subclass of HelloSignException that might be used to denote a resource that was not found

[mashley806]

I 2nd this request. It would be great if HelloSign could throw different exceptions for different events. For example, a couple of weeks ago when AWS was down our end users couldn't sign documents and we were just displaying a generic issue occurred prompt. It would be great if HelloSign could throw a HelloSignMaintenanceException which we could catch and show the user a more friendly meaningful message.

Thanks for your consideration. Matt

[Framinus]

The following exception is thrown for the error message body when a 409 status code is returned:

Caused by: org.json.JSONException: A JSONObject text must begin with '{' at character 0
at org.json.JSONTokener.syntaxError(JSONTokener.java:410) ~[hellosign-java-sdk-4.0.9-jar-with-dependencies.jar!/:?]
at org.json.JSONObject.(JSONObject.java:179) ~[hellosign-java-sdk-4.0.9-jar-with-dependencies.jar!/:?]
at org.json.JSONObject.(JSONObject.java:402) ~[hellosign-java-sdk-4.0.9-jar-with-dependencies.jar!/:?]
at com.hellosign.sdk.http.HttpClient.asJson(HttpClient.java:206) ~[hellosign-java-sdk-4.0.9-jar-with-dependencies.jar!/:?]
at com.hellosign.sdk.HelloSignClient.createEmbeddedRequest(HelloSignClient.java:797) ~[hellosign-java-sdk-4.0.9-jar-with-dependencies.jar!/:?]