Into the Maelstrom: Music, Improvisation, and the Dream of Freedom before 1970 By David Toop Bloomsbury, 330 pp.   Even given the relative expanse of a projected two-volume history of improvised music, David Toop has set lofty goals for himself. In volume one, Into the Maelstrom: Music, Improvisation, and the Dream of Freedom before 1970, he discusses a number of musical figures from improvising communities: Derek Bailey, Evan Parker, Steve Beresford, Keith Rowe, Ornette Coleman, and Eric Dolphy are a small sampling of those who loom large. John Cage is a totemic figure discussed from a variety of angles. Such