Read MIT Annotations

[withmywoessner]

Reference issue (if any)

Fixes #12660.

What does this implement/fix?

Adds the ability to read WaveForm Database (wfdb) annotations using the already existing library. My proposed API adds two new parameters to mne.read_annotations() fmt and suffix. fmt and suffix are used in combination to read an annotation whose file suffix is not strictly defined.
If mne.annotations(fmt='wfbd'...) is called with no suffix, then the function will check to see if the suffix matches a default list of suffixes.
If mne.annotations(fmt='wfbd', suffix='seizures'...) is called, then the function will bypass the default list of suffixes.

[withmywoessner]

Hi @drammock and @larsoner, I know you mentioned reading the annotations using a predefined list of suffixes in #12660, but I thought it would be useful to also allow for the option to read files using any suffix. Let me know if you prefer otherwise.

[withmywoessner]

Where is the best place to list the suffix mappings @larsoner? The WFBD library mentions a few that I would also like to include besides .seisuzes.

[larsoner]

Where is the best place to list the suffix mappings @larsoner?

Looks like the mapping currently lives here

mne-python/mne/annotations.py

Line 1203 in b38385e

readers = {