Integrate CMake with <catch2/catch.hpp> include paths

This also goes for pkg-config installed by our CMake installation.

This includes

* Updating CMake version on Travis
* Adding a `Catch2` subfolder to the `single_include/` folder to
provide this include path both _inside_ the repository, and _outside_.
* Updated examples to build with the new paths
* Other general CMake cleanup

scripts/updateWandbox.py

@@ -34,7 +34,7 @@ def uploadFiles():
         'code': main_file,
         'codes': [{
             'file': 'catch.hpp',
-            'code': open(os.path.join(catchPath, 'single_include', 'catch.hpp')).read()
+            'code': open(os.path.join(catchPath, 'single_include', 'catch2', 'catch.hpp')).read()
         }],
         'options': 'c++11,cpp-no-pedantic,boost-nothing',
         'compiler-option-raw': '-DCATCH_CONFIG_FAST_COMPILE',