This removes one #define from each unit test file and ensures
consistency between file and module names. This consistency, was not
strictly maintained before. I hope that any discrepancies were
unintentional and that a 1:1 mapping is actually what is desired.
Since the definition is now done at one single place, it would be easy
to apply transformations like removing the 'test_' prefix or replacing
'_' with '-' if this should be desired.
The conditional inclusion of either the library or the header-only
version of the Boost.Test header wasn't tremendously useful in practice
because the tests/CMakeLists.txt file would unconditionally add compile
definitions to basically fore dynamic linking.
This patch adds feature detection to the tests/CMakeLists.txt file to
determine whether to use dynamic linking, static linking or the
header-only version (in that order of preference, for best performance).
The automatic detection could be overridden if needed by defining the
TOML11_WITH_BOOST_TEST_{HEADER,STATIC,DYNAMIC}
variables on the CMake command line.
While we are at it, instead of having a conditional
#define BOOST_TEST_NO_LIB
in each unit test file, handle this once in the CMakeLists.txt file.
