Issue reading configuration file

[tusharm]

Hi,

I'm trying to use this library inside a Spring Boot application.

Since Spring Boot packages the application resources in a certain way, it reads them differently (see https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/core/io/ClassPathResource.html). In contrast, com.createsend.util.Configuration uses java.lang.ClassLoader to load its config file and hence doesn't work in a bundled Spring Boot app.

Ideally, the Configuration object should allow setting individual properties via the constructor. Whether these properties come from file or env vars or somewhere else, should be left to the client.

What do you guys think?