Apple usually hints at the content of its media events via the design of the announcement — but never says up front what's going to be announced. The invitation for tomorrow's event in New York City appears to have a chalkboard theme, indicating a focus on education. Now Bloomberg has posted a detailed news story that apparently confirms some of the rumors that have been going around. It seems that Apple is going to jump headlong into the $10 billion/year textbook industry, with a focus on K-12.