MkDocs, Readme, Files API, Automated session saving, v2.0.1

MkDocs: sphinx docstrings rewritten to google, improved config, written the major part of how-to.
Readme: centered title + logo, added badges, features list, updated changelog.

Improved Files API, added automatical session saving and restoring to Client.
Some changes in makefile and gitignore.
License Notice now refers to all contributors.

docs/reference/atclient.md

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+## `atclient` (Entry point)
+### ::: python_aternos.atclient

docs/reference/atconf.md

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+## atconf
+### ::: python_aternos.atconf

docs/reference/atconnect.md

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+## atconnect
+### ::: python_aternos.atconnect

docs/reference/aterrors.md

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+## aterrors
+### ::: python_aternos.aterrors

docs/reference/atfile.md

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+## atfile
+### ::: python_aternos.atfile

docs/reference/atfm.md

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+## atfm
+### ::: python_aternos.atfm

docs/reference/atjsparse.md

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+## atjsparse
+### ::: python_aternos.atjsparse

docs/reference/atplayers.md

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+## `atplayers`
+### ::: python_aternos.atplayers

docs/reference/atserver.md

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+## `atserver`
+### ::: python_aternos.atserver

docs/reference/atwss.md

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+## atwss
+### ::: python_aternos.atwss