IPPL-2.3.0

Major Changes

• Boost dependency is removed and we use std::chrono for the timers instead of boost timers. Only the wall time
  is measured and reported.
• FFT interface updated to include new options from heffte v 2.2.0. Also, the updated interface can do Sine and Cosine
  transforms.
• Solvers submodule is merged in to the IPPL repo itself. This is for simplicity. Consequently a new cmake flag ENABLE_SOLVERS has to be turned on to compile the solvers.
• The plasma physics mini-apps from the ALPINE project has been moved to a separate directory named alpine. The idea behind this is test directory is supposed to be a playground for testing things and ALPINE is an application based on IPPL. A new cmake flag ENABLE_ALPINE needs to be turned on for compiling these mini-apps which in turn requires ENABLE_SOLVERS=ON and ENABLE_FFT=ON.

Minor Changes

• The cmake flags ENABLE_IPPLTESTS and BUILD_UNIT_TESTS have been changed to ENABLE_TESTS and ENABLE_UNIT_TESTS for consistency reasons.