Update: Change --substitute short parameter from -s to -S for iki_read.

Update: Change --substitute short parameter from -s to -S for iki_read.

A lot of recent bug fixes have resulted in significant behavioral changes in the iki_read parameters.
There are enough breaking changes at this point that I feel safe in making this change from `-s` to `-S`.

This change makes iki_read more forward compatible with changes introduced in the 0.7.x and greater versions of iki_read.
The `-s` or `--select` from the 0.7.x branch is not being back ported but it is much more compatible to make the `--substitute` short parameter consistent across those releases.