Original PNG files renamed.

96.xcf created with only the letters and numbers inverted, no changes
made to any of the borders.  This file will be used to generate all
the active PNG files.
Completed individual letter and number  inversion in 96.xcf.

Converted to PNG and then scaled that down to create all the rest.  It
may or may not prove to be better to make individual XCF files for
each size in the future and simply convert them, but this should
suffice.