Manual:Messages API

Problems with current message system:
 * Many function with many parameters are confusing
 * The simple case is complicated to do
 * The simple way to do is wrong (wfMsg)
 * wfMsg replaces variables after {{-transform, does not parse nor escape
 * When fallbacks message is used, parsing in wrong language can lead to really broken results. Think about language which has three plurals – english definition has only two, but it is parsed with the interface language. It used to be worse before all plural functions were made to use the last supplied value if there is too few given. This also affects other language dependent stuff like grammar.
 * replaceafter affects all parameters, where it is usually needed only for some of them
 * parsemag (or {{-transform, escape, parse, parseinline... hard to get it right

Suggested solution for all problems above expect parsing in a wrong language, since that problem is much deeper.

See includes/Message.php in trunk...