THELONIOUS HIMSEL(LPOn each of his first three recordings for Riverside, Thelonious Monk included a solo piano presentation, and for many listeners, these were the highlights of each recital. And so it was decided that Monk's fourth Riverside recording, Thelonious Himself, would be composed entirely of solo interpretations; well, almost. Like a great actor finding heretofore obscure layers of meaning in a familiar soliloquy, Monk takes familiar themes such as "April in