Mutil 1.76.6 released

CHANGES
- Fixed various compiler warnings
- Fixed last zero-length read when --double-buffer enabled
- Fixed improper off_t parsing of various options
- Fixed offset of last posix_fadvise on write buffer
- Fixed unaligned file offsets during --direct-read
- Fixed alignment multiple, which must be higher than open man page states
- Added ability to set posix_fadvise as default in reads and/or writes