Basic JSON schema assertion

[mariacamenzuli]

Should resolve #13

[KPull]

Good merge request. Before I can accept it though, I need you to apply the following fixes, please:

• Use the correct encapsulation for your class members. In particular the field expectedSchema should be private and the constructor JsonSchemaAssertions should be protected.
• Remove all the unnecessary final qualifiers from your fields, parameters and variables.
• I can see smaller logical chunks in the execute() method such that it can be split into smaller methods: parsing the JSON response and validating it against the schema are two different things happening in that method.
• You need to add test cases for:
  • Constructing a JsonSchemaAssertions using a String; and,
  • The parsed JSON response is not correct against the given schema.

[KPull]

Merged! Thanks a lot! :)