Preliminary work on more examples. Also move string_view to separate header to better separate concerns. Also work on example infrastructure.
Minor edits.
Put initial infrastructure in place to generate tutorial example code from the actual source files in the btree/example directory.
Add extract files.
Add infrastructure.
Infrastructure
Add example snippet markers
The tutorial extraction of example code from .cpp source files infrastructure is now working. A VC++ solution to build the example programs is in place and working, although more work needs to be done on the individual example programs. This is sufficient progress to now merge the private feature branch into develop.