Output metadata for each word set

[jonadsimon]

Word-set metrics:

• number of words
• true packing value (not upper-bound)
• mean word length <-- very important
• mean pairwise overlaps
• total pairwise overlaps <-- very important

Solution-board metrics:

• number of horiz/vert/diag/fwb/bwd words
• number & % of overlapping letters
• number & % of rows/columns with overlapping letters

[jonadsimon]

Code now returns word-set metrics. Still need to return solution-board metrics.

[jonadsimon]

Updated in https://github.com/jonadsimon/wonder-words-generator/commit/d552718972e50019104df16d003796a30a59e575

Still don't have overlap counts, but good enough