[PATCH] configure: add --without-api-docs option

[David Bremner]

mp39590 at gmail.com writes:

> From: Mikhail <mp39590 at gmail.com>
>
> Add option to explicitly disable API man page build even if doxygen
> binary is available. --without-docs also implies not building API
> manpage.
>
> This change intended to add more distinctness into build system and
> allow user not to build unwanted man pages.

pushed to master