Implement environment variables in a standardized way.

[Poikilos]

Using URL[$e] (at least for new shortcuts) will make the format more standardized. The new standard way of doing this (at least known to work in KDE) is by using [$e] to enable environment variables:

[Desktop Entry]
Type=Link
URL[$e]=$HOME/Documents/unnumbered/Spirits of Namaman.png

The separate mimetype will still be necessary for the following cases:

• For cross-platform compatibility (such as when using Nextcloud)
• When using ~ to represent HOME
• When using variables when on windows.

The following doesn't work according to standards, but for backward compatibility with older versions of blnk, it could be forced to work:

[Desktop Entry]
Type=Link
URL=$HOME/Documents/unnumbered/Spirits of Namaman.png

• fails since [$e] is required to enable environment variables

GNOME doesn't support $e: https://forum.kde.org/viewtopic.php?t=32909, but blnk could overcome this by having its own MIME type for shortcuts.

For the most compatibility, $e could be excluded when not necessary as per issue #3.