Add interacting pairs option

[zktuong]

addresses #71

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.05%. Comparing base (1fec535) to head (e74207e).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #72 +/- ## ========================================== + Coverage 97.03% 97.05% +0.01% ========================================== Files 7 7 Lines 674 678 +4 ========================================== + Hits 654 658 +4 Misses 20 20 ``` | [Flag](https://app.codecov.io/gh/zktuong/ktplotspy/pull/72/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zewen+Kelvin+Tuong) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/zktuong/ktplotspy/pull/72/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zewen+Kelvin+Tuong) | `97.05% <100.00%> (+0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zewen+Kelvin+Tuong#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files](https://app.codecov.io/gh/zktuong/ktplotspy/pull/72?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zewen+Kelvin+Tuong) | Coverage Δ | | |---|---|---| | [ktplotspy/plot/plot\_cpdb.py](https://app.codecov.io/gh/zktuong/ktplotspy/pull/72?src=pr&el=tree&filepath=ktplotspy%2Fplot%2Fplot_cpdb.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zewen+Kelvin+Tuong#diff-a3RwbG90c3B5L3Bsb3QvcGxvdF9jcGRiLnB5) | `93.57% <100.00%> (+0.10%)` | :arrow_up: |