Change sources getting method.

- Rather than defining the urls where they are gotten (python sysa,
  python sysc, inside sysc), a spec file is now used that is easily
  interpretable and tool-independent.
- This is interpreted by rootfs.py and inside sysc.
- This is also used to make sources available and extract sources.
- Manual dirname selection is no longer required as is tarball renaming
  upon download - all of this is handled automatically.

Fixes #188

sysa/e2fsprogs-1.45.7/e2fsprogs-1.45.7.sh

@@ -2,16 +2,12 @@
 #
 # SPDX-License-Identifier: GPL-3.0-or-later
 
-src_unpack() {
-    default
-
-    # Get remaining utf files
-    cp ${DISTFILES}/*.txt ${pkg}/
-}
-
 src_prepare() {
     default
 
+    # Get UTF txt files
+    cp ../*.txt .
+
     # Rebuild libtool files
     rm config/config.guess config/config.sub config/ltmain.sh
     libtoolize -i