Show_Submission/extract_images: removed unwanted modules, added POD
documentation, added 'coalesce' routine, adjusted to use the
absolute paths to the input files and generated image files. The
latter are always written to the directory where the HTML resides.
Corrected logic around overwriting image files and '--force'.
Still an 'alpha' version subject to more testing.
Show_Submission/extract_images: new script to read an HTML file looking
for 'data' scheme URIs (embedded images), extract them and modify
the HTML to reflect the new source of the image. At present it
writes a generated file name with a sequence number in it, but the
appropriate suffix/extension for the image type. This is an alpha
version which needs further work.
Show_Submission/parse_JSON: attempting to debug a JSON parsing failure.
