It can’t be easy to invent a brand-new fairy tale; even James Lapine and Stephen Sondheim had to rely on the old favorites. But here comes Jason Woods, not only cobbling together an entirely original fantasy with The Near Disaster of Jasper & Casper, but performing all the parts, with distinctive voices and personalities for all the characters. Woods may seize on some familiar plot points, and he’s not always tidy: “Jasper and Casper” don’t rhyme perfectly with “Disaster,” as he seems to have been aiming for. But he knocks himself out to engage the audience.