Smart grouping in updated file list

[Quincunx271]

Implement semi-smart grouping in the generated file list. In other words, groups of files are separated by blank lines:

# Before this change:
set(sources
    # sources
    some/path/to/file1.cpp
    some/path/to/file2.cpp
    some/path/to/file3.cpp
    some/other/path/to/file1.cpp
    some/other/path/at/file2.cpp
)

# After this change:
set(sources
    # sources
    some/path/to/file1.cpp
    some/path/to/file2.cpp
    some/path/to/file3.cpp

    some/other/path/to/file1.cpp
    some/other/path/at/file2.cpp
)

There is a latent bug: .\bin\existing.exe runs forever on Windows, and I have no idea why. I couldn't get my debugger to show me the source. Edit: The problem is that fs::ascending_iterator{} produces "/" on Windows, but you can't get higher than "C:\", so find_if keeps going.

Other changes:

• Use Range V3, but not version 0.4.0, rather the most recent commit. This is because MSVC is only supported on some commit after 0.4.0. Once Range V3 has a new release, we can use conan.
  • I used FetchContent to obtain Range V3 (along with aliasa.io to show some love to slurps-mad-rips) rather than embedding the rather large repo into pitchfork.
• Use the Catch2 package hosted by catchorg rather than bincrafters. Since there is a Catch2/XXX@catchorg/stable and catch2/XXX@bincrafters/stable, there are problems on Windows because conan can't handle the clashing names caused by the case-insensitive filesystem.