Adding merge_event function

[ater49]

Adding merge_event in order to merge two similar events in one.

[codecov]

Codecov Report

Merging #202 into master will decrease coverage by 0.12%.
The diff coverage is 12.5%.

@@            Coverage Diff             @@
##           master     #202      +/-   ##
==========================================
- Coverage   64.28%   64.16%   -0.13%     
==========================================
  Files          23       23              
  Lines        3408     3416       +8     
==========================================
+ Hits         2191     2192       +1     
- Misses       1217     1224       +7

Impacted Files	Coverage Δ
pymisp/api.py	47.06% <12.5%> (-0.25%)	⬇️

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[Rafiot]

This new method will be very confusing:

• It doesn't copy the objects
• What is supposed to happen if we have duplicate attributes/objects?

iirc, there is a merge event functionality in MISP. I think it would be better to open up this one to the API, so we stay consistent. @iglocska what do you think?

[ater49]

Didn't see that function. I can close this PR and work to implement the existing core functionality.

[Rafiot]

We have something much better than merging events in the 2.4.90 release: MISP/MISP@caf53e0

It let's you extend an event with an other event without modifying the original one. It is especially useful then said event isn't yours.

Does it fits your needs?

[ater49]

It fits!

I close this PR