Allow defining xHTTP verbs

Signed-off-by: Christophe Vanlancker <christophe.vanlancker@inuits.eu>
Correct usage of http_verbs and document them

Signed-off-by: Christophe Vanlancker <christophe.vanlancker@inuits.eu>
Do not surround httpverb int with quotes

Signed-off-by: Christophe Vanlancker <christophe.vanlancker@inuits.eu>
Fix some indentations and add support for number of threads

Signed-off-by: Christophe Vanlancker <christophe.vanlancker@inuits.eu>