mbuf: additional functions
mbuf: additional functions

- mbuf_get_char
- mbuf_get_chars

same as _byte/_bytes but for char type

- mbuf_get_uint64be
- mbuf_slice
- mbuf_copy

mgjv/libusual,rabbitt/libusual,ifduyue/libusual,ifduyue/libusual,markokr/libusual,markokr/libusual,rabbitt/libusual,mgjv/libusual,ifduyue/libusual,markokr/libusual,ifduyue/libusual,mgjv/libusual,markokr/libusual,rabbitt/libusual,rabbitt/libusual,mgjv/libusual