Add custom headers

[mgrottenthaler]

Pull Request Template

Description

Adding parameter for custom headers. Described in #33

Fixes # #33

Type of change

Please delete options that are not relevant.

• [x ] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• No parameter supplied (nothing changed)
• Parameter without colon supplied (> error)
• Correct parameter supplied e.g. "Test: Test"

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes (existing ones yes, but I don't really understand how to add unit tests, I think humble has to be rewritten to allow easier unittesting)
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings