fix compilation error in core_io.h

- error: 'vector' in namespace 'std' does not name a type
- add <vector> include in core_io.h
- remove <vector> includes from core_read.cpp and core_write.cpp
add license header to core_io.h, core_read/_write.cpp
Declare SignatureHash() in script.h
URLs containing a / after the address no longer cause parsing errors.