Changes

Summary

1. added lemmas
2. corrected some URLs
3. permissive Doc.dirs: some entries may be absent due to distribution bootstrap, e.g. $JEDIT_HOME/dist/doc;
4. merged
5. updated polyml component -- omitting bad polyml-5.7.1-3;
6. use preferred resolver according to DOI Handbook §3.8
7. no --enable-shared for x86_64-darwin: does not work on some test machine;
8. proper target directory;
9. tuned;
10. more robust options;
11. back to --disable-shared on windows to avoid odd core-dump of polyimport;
12. tuned;
13. back to --disable-shared on x86-darwin to avoid odd core-dump of polyimport;
14. clarified command-line defaults;
15. enforce shared libpoly on all platforms, with File.copy before File.move;
16. NEWS;
17. updated to polyml-5.7.1-2, which includes libgmp for x86-darwin as well;
18. support for libgmp for x86-darwin;
19. more accessible src/Pure/ROOT.ML;
20. tuned;