fold_events accepts keywords and ignores them

[matteobachetti]

Description of the Issue

A recently reported bug showed that people were using the fdot keyword in fold_events. This keyword does not exist, but the function is accepting it and ignoring it due to the use of **kwargs. Using such a name for this keyword is understandable, as it's used in other functions, and not having an error people assume it's correct.

Your suggestions for the Fix

I suggest adding a check and a warning, or even a ValueError, for ignored keywords.

[spranav1205]

Hi,
I have written a fix for this, PR #837. I noticed that fdot is a parameter, although it does not need a keyword to be passed.
The description of the function mentions this, but it might not be clear to the user.

[matteobachetti]

Resolved by #837