Updates containing:
   - updates to make AnalysisBaseExternals build out of the box on top of macOS High Sierra with Xcode 9.0;
   - the ability to override (from the command line) which LCG version the LCG using external projects should build against;
   - a fix for building lwtnn on platforms providing an acceptable version of Boost, like Ubuntu 16.04;
   - a small fix for BAT to build correctly against LCG_91.

Update containing:
   - Explicit builds of XRootD and DCAP for the standalone build of ROOT;
   - Addition of the lwtnn external for the analysis and offline releases;
   - Small fix to reduce the lines printed by AthAnalysisExternals;
   - Some updates to the GCC checkers code.

Tagging the following changes in the 1.0 branch:
  - Made the ROOT build work out of the box on MacOS.
  - Included the updates made in the package selection code. Printing loud warnings when the user made a mistake.
  - Added a whole bunch of copyright statements to all the files, now that the repository is globally visible.
  - Added the build of LHAPDF to AthDerivationExternals.

Tagging the latest updates for making the AnalysisBaseExternals build more robust, and getting rid of a warning during the build of dSFMT.

Tagging the update made to the ROOT build, meant for AnalysisBase/AnalysisTop. For a more robust setup in grid running.

Tagging the following updates for 21.X:
  - Made the BAT build not rely on RooStats. To make it a bit easier to use against custom-built ROOT versions.
  - Updated the way status messages are printed while the `atlas_project` function reads in the configuration of all packages. To make the printouts in a partial build less overwhelming.
  - Updated the ROOT build to use its built-in GSL version.
  - Updated AthAnalysisExternals and AthSimulationExternals not to build code in a multi-threaded way.

Tagging the 1.0 branch with the following updates since 1.0.15:
  - Synchronised Eigen to build the same version (3.2.9) that's in LCG_88;
  - Included various CMake updates in AtlasLCG;
  - Added the PyAnalysis package, to provide NumPy for AnalysisBase;
  - Added DMTCP to the AthDerivation externals (to keep AthenaMP functional once the 21.0 updates get merged in);
  - Added BAT to the available externals, to be used by AnalysisBaseExternals. (AnalysisTop most of all.)

Tag adding dmtcp to AthSimulationExternals, making AtlasLCG a bit more robust, and bringing
with it some documentation updates.

Tag fixing the python setup issues that crept into 1.0.13. Making it impossible
to build Gaudi on top of certain projects of the repository.

Tag introducing AthAnalysisExternals, and updating the analysis releases to LCG_88.
It also introduces FastJet-3.2.2, and makes AnalysisBaseExternals build Python on
MacOS X by default.

Upgrading to LCG_88, and some other updates.

This tag brings with itself LCG_88 for all LCG using projects,
a new external (dmtcp), and some dictionary generation fixes.

Tagging the updates to the dictionary handling code. Fixing the CI build issues
encountered recently.

Adding the setting of the TDAQ_PYTHON_HOME and TDAQ_VERSION variables to the runtime
environment for projects using tdaq-common and tdaq respectively.

Now explicitly setting the GCC optimisation flags for Debug, Release and RelWithDebInfo builds.

Tagging the FindXrootd.cmake fix, to make it easier to collect the new
version of the code into the 21.X builds.

Creating the first 21.X specific tag from the 1.0 branch. This should be in
sync with the externals that were compiled into AtlasExternals-21.0.20.

Creating the last tag before creating a separate branch for the 21.X releases
built from the athena repository.

Tagging the latest version with the GCC checker and ReleaseData
updates included.

Tagging the latest version, fixing a problem in the Boost build, and removing an incompatibility introduced for ZSH previously

Tagging the update to how the multi-versioned externals are set up for the build of the offline projects