add methods to export results in tabular format

[liannette]

• add method to nplinker class for exporting links, as well as genomic and metabolomic data
• add test for generating the tabular data for the links

[CunliangGeng]

Please assign me to review it when it's ready ;-) If you're still working on that, it's better to change it to a draft PR

[liannette]

I thought I was finished, but I realized that it still needs a bit of work. I will assign you as soon as I'm happy with it!

[liannette]

@CunliangGeng It's ready for review :) I just can not request a review explicitly, because I have only read permission for the repository.

[CunliangGeng]

Let's check the code step by step, and first thing to check is about code format and style:

1. Please check the errors in the static typing, and correct the incorrect typings. You could use mypy to check them locally before committing.
2. It is not explicitly mentioned, but we do follow some rules for the order of methods/functions in a class/file. The order of methods/functions are:

• __init__ method
• other magic methods, e.g. __str__
• property methods (using @property)
• regular methods, class methods (using @classmethod), static methods (using @staticmethod)
• private methods (_func )
• deprecated methods (using @deprecated)

For the same level of methods, e.g. regular methods, it's recommended to order them in alphabetical order.

Please check the new methods/functions you added and put them in the right place.

[CunliangGeng]

Please check the comments in each file.

Last time I mentioned that for the same level of methods, e.g. regular methods, it's recommended to order them in alphabetical order. Well, I forgot to mention that it's better to cluster and order the methods based on their purposes, e.g. it's intuitive to put the input/read/load methods before the output/write/save/dump methods regardless of their names.

Also, please do not change the order of existing methods in this PR, it's better to do it in an independent PR.

[CunliangGeng]

This PR needs changes before approval ;-)

[liannette]

I just looked through your comments, they are quite helpful, thanks!

[CunliangGeng]

Two more suggestions:

1. You could use Github Desktop to mange your local commits (e.g. reorder and squash/combine them) with ease. This practise could make the commits more organised, which will make it easier to understand your changes and facilitate the review process.
2. The PR basically could be split to 2 or more smaller PRs to make each PR more atomic and faster to review. For example, the changes to bgc.py is independent, which could be done in another PR. You don't have to split this PR now. Next time, when there are independent/irrelevant changes, please consider putting them in another PR.

[liannette]

I integrated the requested changes, except the ones in the unresolved conversations. Can you take a look at my replies there?