Fix escaping of asterisks in AQL documentation.

Asterisks need to be escaped with backslashes, but if surrounded by square brackets, the brackets need to be escaped as well. (Please test, github's markdown parses seems to be unable to do this at all, unless html tags are used.)

An italic list expander <i>[\*]</i> needs to be written as: `*\[\*\]*`

Does not apply to parentheses it seems, but maybe other characters with special markdown meaning.