helpconstants: add paragraph explaining += in assignments
matcher: add support for function definitions (fixes #81)
matcher: consider { } part of the function definition
matcher: remember defined functions and match accordingly (fixes #81)

we keep track of which functions are defined and try to match commands against
them before looking up a manpage.

this trick makes the results for the forkbomb make some sense ;)
index: use a macro for generating examples html