If output argument is not given the input filename is used with different extension
Ignores coverage folder
Adds rspec and folder structure to project

* renames `Converter` to `Eson::Transform::Generator` class
* adds test setup with simplecov code coverage
* extracts requires to transform specific classes to a file
Changes order of gem requires, fixes running of tests with riot
Adds a sample API documentation JSON file for cluster.health
API class allows to set an enum parameter with name, values and default

* adds specs to check if `parameter_enum` method adds an attribute with enum values
* adds generator specific specs to check if generated Ruby class is correctly created
* adds helper method to load an API description sample file