Get rid of global macros; they break old articles

For example, blosxom-macros.blog discusses the ^2 macro, and we don't
want it turning into <sup>2</sup> just because that's listed in the
global macros file.  Any time a macro was added to the global file
would have the potential for totally breaking a lot of old articles.

Instead, introduce a #load directive.  "#load foo" pauses and tries to
load macros from the state/macro-foo file.  The old global macros file
is now macro-std, loaded via "#load std".  The '#load' directive does
not appear in any extant article.