Having git submodules as source makes making releases really really
hard, since submodules are not included when downloading a tarball
from the git repository host.
The idea now is to keep a submodule of tllist under 'external', and a
static copy under 'subprojects'.
This means builds will use the static copy, while having easy access
to the git submodule makes it easy to update the static copy (git
submodule update --remote + cp -r)
