Adds a British English writing-conventions skill covering -ise/-our/-re/-ence/-ogue spellings, doubled-l verb forms, programme vs program, punctuation (single quotes, logical punctuation, spaced en dashes, Oxford comma), vocabulary, dates/times, grammar (collective nouns, shall/will, prepositions, present perfect), measurements and currency. Polishes a few entries on second pass: doubled-l wording, mediaeval note, en-dash example, and 'informal' label.
