GIANT CLUSTERFUCK OF A COMMIT

OK, this is epic.  I was basically just trying to a) support Clang and
b) add more test coverage.  _THREE MONTHS_ and a few hundred CI runs
later, this is what I came up with.  I don't know how it ended up being
what it is, but here we go.

Some highlights of the changes:

1) CI builds has been moved to GitHub Actions,
2) the entire notion of a toolchain has been reworked; it now supports
Clang on all platforms.

* .github: this directory contains the GitHub Actions workflow
scripts/actions.  In the process, I created like 6 external GitHub
actions, but it's still pretty massive.  An upside is that it covers
much more platform/toolchain combinations _and_ check a lot of the
expected post-conditions.  TODO: .ci/Makefile is obsolete now, as well
as .travis.yml and .appveyor.yml.

* common.cmake: added Clang support.  In the process, a great deal has
been learned about how CMake works; in particular, static runtime
support has been reworked to be more robust.

* project: the entire notion of a "toolchain" has been reworked.
Instead of a measly --mingw parameter, there's now a separate --toolset
parameter, which allows you to choose between GCC, Clang, MSVC, etc.
Both Boost and CMake build scripts were enhanced greatly to support
Clang and other toolchains in a more robust way.

1 files changed, 6 insertions, 4 deletions

diff --git a/examples/boost/foo.cpp b/examples/boost/foo.cpp
index 3bd0326..6219e68 100644
--- a/examples/boost/foo.cpp
+++ b/examples/boost/foo.cpp
@@ -3,9 +3,11 @@
 #include <iostream>
 
 int main(int argc, char* argv[]) {
-    std::cout << "Hello from "
-              << boost::filesystem::absolute(boost::filesystem::path{argv[0]})
-                     .string()
-              << "!\n";
+    namespace fs = boost::filesystem;
+    std::cout << argv[0] << '\n';
+    for (int i = 1; i < argc; ++i) {
+        std::cout << fs::absolute(boost::filesystem::path{argv[i]}).string()
+                  << '\n';
+    }
     return 0;
 }