Add an option to disable modules by name (or group?)

Handle arbitrarily nested modules (find modules -name modinfo.txt)

Flatten outconfig output:

  Enabled
    ciphers:
    hashes:
    macs:
    <etc>

  Disabled:
    ciphers:
    hashes:
    macs:
    <etc>

Move most code into modules
 - Much ifdef

Fix the macros, extension doesn't seem right

 BOTAN_HAS_*?

Move src/* to src/corelib ?
Move modules/* to src/*
rmdir modules

Further splits (some modules requiring others)
   RNGs

   RSA, RW, DSA, ElGamal NR, DLIES, DH
   BigInt itself
   X.509/PKCS #10
   ASN.1 modules


 Finally the 'core module' baselib consisting of
   base classes, libstate, allocators, etc,
   which requires (or detects and uses) other modules

Move default mlock/mutex code as if modules
  (may need configure changes to avoid conflicts)