keep a map of the LIKE expressions for each category
produce a hash of all the chains keyed by author
cache the list of bins for each category
use the cached list of bins
the hash returned by _find_authors_chains should only contain authors that have chains
the proper contest name is 'all-time', not 'all-times'
_compute_boards_current replaces _find_current_chains

this is using the chains found by _find_authors_chains
_compute_boards_alltime produces the results for the all-time boards
update-boards now computes all the boards for the site
factor out the code to commit entries to the once_a boards
keep one entry per author for the all-time contest
_commit_entries will assume entries are sorted