xmlsec 1.3.x: switch xmlSecSize to size_t, etc (breaks binary ABI)

[lsh123]

Want to fix:

1. xmlSecSize should be typedef to size_t
2. xmlSecByte should be typedef to unsigned chat
3. XMLSEC_SIZE_BAD_CAST should go away
4. Remove soap code
5. TBD

This breaks ABI compatibility so

1. provide --enable-xmlsec-compat-12x mode (and similar for Win32 build) with default -- disabled
2. bump release to 1.3.0
3. publish release 2-3 months early than usual schedule for testing