Differences between two METHODS reports

#### Characteristics
- **Issue Type**: feature
- **Severity**: feature
- **Tool/Service/Component**: PitMP

#### Description
Given two `METHODS` reports get the methods that change their classification.
If no report is given, then use the two latest reports in the PIT output directory.
Generate a `JSON` file to help automation and  an `HTML` file for human readability. 
