Some suggested corrections for the wx documentation.

Here are some suggested corrections for the wx documentation.

There are also some more things which I would suggest, but aren't in this patch:
1) _fun_ is sometimes emphasised, sometimes not... _I_ think it should always be emphasised.
2) API, GUI and Erlang is written in lower case. _I_ think API and GUI should use upper case, and Erlang should start with an capital E.