PLUGIN METADATA TAGS
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id                  the key; C++ library base name or Python module name
plugin_id           for the official repository: an integer id. At the time, used for voting only.
name                human readable plugin name
description         short description of the plugin purpose only
about               longer description: how does it work, where does it install, how to run it?
category            isn't it depreciated?
tags                comma separated, spaces allowed
changelog           may be multiline
author_name         author name
author_email        author email
homepage            url to the plugin homepage
tracker             url to a tracker site
code_repository     url to the source code repository
version_installed   installed instance version
library             absolute path to the installed library / Python module
icon                path to the first of (INSTALLED | AVAILABLE) icon
pythonic            true | false (is plugin pythonic or cpp?)
readonly            true | false (is core plugin?)
installed           true | false
available           true | false
status              not installed | new    |   upgradeable | orphan | downgradeable *
error               NULL | broken | incompatible | dependent
error_details       error description
experimental        true if experimental, false if stable
version_available   available version
zip_repository      the remote repository id
download_url        url for downloading the plugin
filename            the zip file name to be unzipped after downloaded
downloads           number of downloads
average_vote        average vote
rating_votes        number of votes

* status is only obligatory for Pythin plugins and it must match all the tags:
available, installed. version_available, version_installed.
orphan = installed and not available to download;
new = not installed and seen for the first time;
downgradeable = the available version is lower than installed one.