removed hexdump, added memdump

Cleaned and refactored the memory dump section.

Major changes:
- Removed: hex_quad, hexdump, hexdump_aux, ddump, dd
- Added: memdump, memdump_hex, memdump_ascii

Minor changes:
- Added: $MEMDUMP_..., $CONTEXTSIZE_STACK_DIRECTION, $CONTEXTSIZE_DATA_DIRECTION
- Renamed $SHOWSTACK to $SHOWSTACKWIN 
- Renamed $CONTEXTSIZE_* to $CONTEXTSIZE_*_LINES