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/generateSingleHeader.py

@@ -24,7 +24,7 @@ def generate(v):
 
     seenHeaders = set([])
     rootPath = os.path.join( catchPath, 'include/' )
-    outputPath = os.path.join( catchPath, 'single_include/catch.hpp' )
+    outputPath = os.path.join( catchPath, 'single_include/catch2/catch.hpp' )
 
     globals = {
         'includeImpl' : True,