Expand the explanation of citation key patterns

[koppor]

Currently, the description of patterns is short: https://docs.jabref.org/setup/citationkeypatterns#special-field-markers

For authshort, we had following description in the code:

given author names

1. Isaac Newton and James Maxwell and Albert Einstein and N. Bohr
2. Isaac Newton and James Maxwell and Albert Einstein
3. Isaac Newton and James Maxwell
4. Isaac Newton

yield

1. NME+
2. NME
3. NM
4. Newton

We should have a table putting all possibilities together? Or maybe have a table per key.

author list	authorsalpha	authshort	...
Isaac Newton	New	Newton	...

authIniN format

Each author gets (N div #authors) chars, the remaining (N mod #authors) chars are equally distributed to the authors first in the row. If (N < #authors), only the first N authors get mentioned.

For example if

1. I. Newton and J. Maxwell and A. Einstein and N. Bohr (..)
2. I. Newton and J. Maxwell and A. Einstein
3. I. Newton and J. Maxwell
4. I. Newton

authIni4 gives:

1. NMEB
2. NeME
3. NeMa
4. Newt

auth.etal, authEtAl, ... format

1. Isaac Newton and James Maxwell and Albert Einstein (1960)
2. Isaac Newton and James Maxwell (1960)

auth.etal give (delim=".", append=".etal"):

1. Newton.etal
2. Newton.Maxwell

authEtAl give (delim="", append="EtAl"):

1. NewtonEtAl
2. NewtonMaxwell

Note that [authEtAl] equals [authors2]

auth.auth.ea format

1. Isaac Newton and James Maxwell and Albert Einstein (1960)
2. Isaac Newton and James Maxwell (1960)

give:

1. Newton.Maxwell.ea
2. Newton.Maxwell