v1.16.0

• Gaussian beam source feature (#1303 and #1310).

• New API for specifying planewave diffraction orders for eigenmode sources
  and coefficients (#1316).

• More accurate gradients in adjoint code (#1285).

• Simpler Python API for outputting ε or μ at a given frequency (#1374).

• --with-libctl-dir option of configure now accepts simply the installation prefix in addition to prefix/share/libctl (#1286).

• Less verbose mode-solver output from MPB (#1302, #1388), and new
  meep.verbosity option in Python (#1349).

• Bug fix for single-point DFT monitor (#1333).