Don't require plugin key group name and label strings to be static

Take a copy of the strings not to require them to live live as long as
the plugin does.

This is mostly useful for plugins implemented in dynamic languages
(e.g. through a plugin proxy), as most C plugins will use a static
string here; but it makes the API more straightforward and avoids odd
issues if any plugin doesn't use static strings here, even C ones.

Closes #1125.

For example "doc/doxygen_sqlite3.db" is created on Windows/MSYS2.

The location of the file changed since we are using MSYS2.

Update of Slovak translation

Fix fuzzy entries in German translation

Update zh_CN translation

Fixes #1102.

updated it.po for upcoming 1.28

Properly expose TMTag which already contains documented members.

Don't use wildcards that can catch generated files.

While at it, also avoid Doxygen picking up those generated files.

This allows GI-based plugins to traverse/inspect the array and consequently
Geany loaded tags.

tm_tag.h and tm_parser.h contain documented symbols so doxygen shall process
them.

It's members are already documented so it's kind of half-exported anyway.
Since geanygendoc already uses the structure (and I plan on writing a plugin
that requires it too) just make it official.

Broken in #966.

Improve README