Use <time> to label events

HTML 5 introduces tag <time> which defines date, time or both. It's better choice to label events than non-semantic <strong>.
Tag <time> is accompanied with attribute 'datetime' which contains date in machine-readable format.

For compatibility with previous appearance this commit adds time {font-weight: bold} to CSS.
Add divideEvents() function

Function divideEvents() outputs into elements with ids 'fevents' and 'pevents' which are added to index.html

Global effects:
-- Add to prototype Date.yyyy_mm_dd
-- Add to prototype Array.filter and Array.map for old browsers
-- Set divideEvents() as a handler of document.ready event using auxiliary functions bindReady(), onReady()
   and array readyList.
Call events.js in index.html
Remove Makefile