`diffkemp-out.yaml`: Add info about equal/unknown function

[PLukas2018]

Currently, diffkemp-out.yaml contains only information about semantically differing functions. I think it would be good if the file contained information about all the compared functions / sysctl parameters, even those that are equal or unknown or where error occurred. The reason for this is to make it possible to parse all the information from the file without the need to parse other files/stdout.

The updated format of diffkemp-out.yaml remains to be discussed, but it could theoretically look like this:

results:
- function:
  result: non-equal # <--- Added field
  diffs:
  - function:
    old-callstack:
    - name: ...
      file: ...
      line: ...
    - # ...
    new-callstack: 
    - # ...
  - # ...
# Added info about equal, unknown, error functions
- function: my_equal_function
  result: equal
- function: mu_unknown_function
  result: unknown

The results field would newly contain info about all compared functions, and individual functions would contain a new field result which would contain info about the result (equal, non-equal, error, unknown).

---

An approximate list of things that will need to be updated:

• Updating the YamlOutput class so it outputs the updated diffkemp-out.yaml file format.