Summary of changes:

 * Update to C++11 and CMake 3.5 (both are now required).
 * Provide a basic 'make install' target (see documentation).
 * Add a new analyze-rivet stage to analyze showered events with Rivet.
 * Update external libraries:
   * LHAPDF 6.2: add workaround for bug in path handling introduced in 6.2
   * Pythia 8.230: add workaround for a removed function
   * OpenLoops: Set install_path to find process libraries at runtime, including
     support for OpenLoopsPath environment variable.
   * Add support for Rivet (and YODA and FastJet needed by it).
   * Fully encapsulate internally used packages (tinyxml, yaml-cpp)
 * Much more flexible and consistent naming and handling of setup and
   production files, allowing to use different directories and to add separate
   tags for each stage.
 * Allow reading and writing zipped .lhe.gz and .hepmc.gz files (requires zlib).
 * Update Python interface:
   * Improve command-line options (all in --lower-case style).
   * Add a Python cpp_extensions library which directly calls main functions
     and avoids subprocess forking.
   * Improve MPI running and error handling (avoid MPI deadlocks).
 * Improve setup stage:
   * Provide CL options to directly set total points and iterations.
   * Speed up various parts, use MPI for merging steps if available.
 * Several improvements and bug fixes under the hood, most important user-visible ones:
  * Fix a bug in SCET ppV012 calculation that could introduce small biases in
    results due to correlated random numbers.
  * Fix NNLO reweighting factors given in documentation.
  * Fix memory leaks and potential segfaults in rare corner cases.