New skill mainly for semi caster guilds which would allow casting spell when
you are short, not out of, spellpoints. Doing skill would allow casting when
you are at positive spellpoints, but not having enough of them for particular
spell. Skill woud drain lots of EPs and some HPs depending on how much you are
short of SPs.

Full casters wouldn't need this, but semicasters might find it usefull
occassionally. This could be unbalancing. And skill would need to be used
before casting, like ceremony.