Add a Meson option "portable" to choose between "portable" and unix-like
directories. Add information about this option in the README.
To determine the user's directory use the variable USERPROFILE only on
Windows and use HOME otherwise.
Implement the "portable" option in the package build script.
Create the user's config init file if lite user's config directory does
not exists.
No longer use the awkward package.searchers but instead add user's
config dir at the end of package path.
It basically works by setting the data directory to
$prefix/share/lite-xl
where $prefix is determined so that $prefix/bin corresponds to EXEDIR.
The packages 'user' and 'user.*' are loaded from the directory
'$HOME/.config/lite-xl'.
Currently the editor will not work if it is not installed.
There is also a caveat about the 'data' directory which is installed
in the bin directory. This may work but does not seem ok because it is
pollution a shared bin directory and the 'data' folder may not be unique
to Lite.