Correct long option `threshold' required_argument to optional_argument.
Correct short option -T to allow for optional argument -T::
Allow threshold limiter values of 1-99 expressed as a percent of
chunk size.
Ex.
	-T95 would mean that per lzo_compresses, a chunk would need to
	be at least 5% compressible or else continue testing until fail.
Add THRESHOLD option to lrzip.conf.example file
Update man pages
Updates to control structure to add threshold member and set default to
100.
Set default compression level to 7 again.