Asshai!?!

[Lord_of_the_morning]

I was just wondering how much do we actually know about the asshai? I know melisandre Is Asshai....but what do we actually know about them....Can they use magic...I know martin hasn;t give the series much magic....but can asshai actually use magic?.....When melisandre kills renly with teh shadow baby...is that jsut a power given to some chosen by the lord of the light or is that actually magic....I has been buggin me for some time now....

any thought's???