First implementation of unix-like data directory

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'.

src/meson.build

@@ -12,6 +12,7 @@ executable('lite',
     lite_sources + lite_rc,
     include_directories: [lite_include, font_renderer_include],
     dependencies: [lua_dep, sdl_dep, libm, libdl],
+    c_args: lite_cargs,
     link_with: libfontrenderer,
     link_args: lite_link_args,
     install: true,