DOC: additional info for audformat.define

[hagenw]

This adds additional information to the audformat.define module as this contains values that shouldn't be changed as the are part of the audformat specifications and other values that are only recommendations and might be changed by a user.

This is seems to me also a good preparation for including audformat.define.Emotion in a next step as proposed in #314.

As this pull request involves several changes I will only pick a few representatives here.

First I added a general introduction to the sub-module

Then for each of the classes that defines values that are part of the audformat specification I added text describing where those definitions are used and mention that they shouldn't be changed, e.g.

If the audformat specification included a link to the entries in the audformat.define I replaced this by the actual values, as the format specification should be the ground truth on available values and not the implementation, e.g.

If the define values are part of an attribute or return value of a class, I mention there that the expected values are provided by the corresponding class in audformat.define, e.g. for audformat.Scheme.dtype

For classes where the values are not given by the audformat specifications, I mention that they can be changed by a user, e.g.

/cc @schruefer

[codecov]

Codecov Report

Merging #327 (1b95b5a) into master (9077dfa) will not change coverage.
The diff coverage is 100.0%.

Impacted Files	Coverage Δ
audformat/core/database.py	100.0% <ø> (ø)
audformat/core/index.py	100.0% <ø> (ø)
audformat/core/scheme.py	100.0% <ø> (ø)
audformat/core/table.py	100.0% <ø> (ø)
audformat/core/define.py	100.0% <100.0%> (ø)

[hagenw]

I spotted a few minor errors and will set to WIP until I have fixed them.

[hagenw]

I spotted a few minor errors and will set to WIP until I have fixed them.

Fixed typos and removed WIP, it's ready for review now.