fix: many table tests bug

[sergii4]

Fix #29

Solution is to use anchor operator.

Added plenary tests

[sergii4]

@akinsho pleasure is mine! I was looking for opportunity to contribute to nvim community and want to thank you for a chance. I think you are doing a great tool which I started to use!

Those test tests significantly speeded up my development process :)

[marcomayer]

@sergii4 thanks a lot! 👍