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/perl-5.003/perl-5.003.sh

@@ -3,12 +3,6 @@
 #
 # SPDX-License-Identifier: GPL-3.0-or-later
 
-src_unpack() {
-    default
-
-    mv perl5-perl-5.003 perl-5.003
-}
-
 src_prepare() {
     default
 

sysa/perl-5.003/sources

@@ -0,0 +1 @@
+https://github.com/Perl/perl5/archive/perl-5.003.tar.gz 9fa29beb2fc4a3c373829fc051830796de301f32a719d0b52a400d1719bbd7b1