manual-text: make sure URLs are displayed if a link text was provided

When the asciidoc source contain URLs of the form:
    http://example.com[An example website]
the text representation of the manual would only contain:
    An example website
without displaying the actual URL.

This patch adds an asciidoc configuration file that sets the inline macros
for several URL types so that the display becomes:
    An example website [http://example.com]
For URLs where no link text was provided, the display becomes:
    http://example.com


which is the same as before.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>