This commits also adds a script that does the amalgamation of headers
and .cpp files into the distributable version, removes the old
`generateSingleHeader` script, and also adds a very simple compilation
test for the amalgamated distribution.
On systems where the file system has excute permissions, this script was
not marked as executable in a clean git checkout and so could be run
without first changing the permissions. Fixed by setting the relevant
git flag.
As Clara is no longer maintained as a separate project, the
implementation was moved to the internal subfolder of top-level
folder. This removes one folder and avoids potential user confusion.
Also simplified the convenience header checking script accordingly.
