REPL help: @Mod.macro -> Mod.@macro

removed special code for handling macro names which is not
needed any more
Miscellaneous fixes to stdlib docs

Mainly fixed modules annotations (e.g. for
LinAlg functions, FFTW etc.)

Also fixed:

* some misquotings (e.g. `a` -> ``a``)
* some external links
* cosmetics (whitespace, lists, etc.)