guard compilation of examples with a cmake variable to make it optional

Tail call to old exception filter if one exists

In Win32 crash handler, continue executing the old exception filter
after performing log queue flush. This should give more correct/expected
behavior during crash.

In-source native build with Conan

The canonical build scripts for production builds are either the GNU
Makefile or Visual Studio projects, so use those in Conan instead of the
cmake adaptation. Having to install both CMake and Conan just to build a
package seems a bit overkill for such a simple project with no external
dependencies.

Also, since this conanfile is in the source tree, use the
exports_sources approach recommended for that scenario in the Conan
documentation.

Finally, we forbid compiler.libcxx=libstdc++ since that causes ABI
incompatibility.

Update year range for license

q

Fix build error with glibc 2.26 and above

SIGUNUSED has been removed and causes compilation errors. Based on
the name it was probaably never used anyway, so just remove it.

Document stdout_/stderr_writer

Allow public access to the internal worker-thread object

Update copyright for 2016 release

Treat trailing "%%" as "%"

When there were no remaining arguments to format, the normal format-
specifier parsing loop was abandoned and the remaining format-string
data was simply copied to the output buffer. But this caused a weird
unexpected switch from treating "%%" as a single percent to treating it
as the verbatim string.