New and Modified Elements

• Added the ILMATRIX element, which allows fast tracking in periodic systems using an Individual Linear Matrix for each particle. The matrix has momentum and amplitude dependence via coefficients (e.g., chromaticity, tune-shift-with-amplitude) specified by the user. This was inspired by requests from Y. Chae (APS).
• Added start-pass, gradual ramp-on, and high-frequency cut-off filters to the ZLONGIT and ZTRANSVERSE elements. These features were requested by Y. Chae (APS).