PR guidelines

Description
- Please provide an elaborate description of the problem you are trying to solve.
Design notes
- If this is a new feature, please provide design notes on the change which the next developer looking at the code might need to know.
Side effects
- Are you aware of any OS-specific deviations, side effects, unhandled scenarios etc.? Let us know.
Test cases
- Which scenarios have you tested already? A list of commands are welcome.
- You can use genbm.sh to automate bookmark generation for tests.

This is more important than your design or code! Users check this first.

README.md
- New dependencies? Update them under Installation.
- New program option? Update program help under Cmdline options verbatim. The short description in help should be more or less aligned to other option descriptions.
- Add an example, if required under Examples.
- Update Operational notes if your change affects current behaviour, links to environment variables etc.
Man page
- Update program options.
- Add the same example, if you ave added one in README.md.
- Update Operational notes. However, new environment variables go under ENVIRONMENT section.
Completion scripts
- Add new program options to completion scripts for bash, fish and zsh.

Add new program options to a reasonable group.
Single quote, single quote, single all the way!
A single line should be less than 140 chars in length.
No trailing whitespaces.
Avoid append(), extend() and use concatenation if possible.
Use string concatenation than substitution if possible, except (logger) prints.
We have automated linting test but you can also test it by running python3 -m flake8 buku.py and python3 -m pylint buku.py.
Add new API documentation, reasonable code comments.
If possible, add test cases for your new API under tests/. We are Travis integrated.
If possible, squash everything to a single commit.

This temporary manual test case on bukuserver (first version can be found here #647)

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