build: General build refactoring

Add vars.mk for variable sharing across makefiles.
Stub and rename example YAML file and template.
  Content to be re-introduced as support is added.
Move generated C++ to a header file.
Add input YAML path option to configure.

Change-Id: Ia06e392e8b120b1e1d8614046064fa432a6f9e18
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/src/example/example.yaml b/src/example/example.yaml
new file mode 100644
index 0000000..5a798e9
--- /dev/null
+++ b/src/example/example.yaml
@@ -0,0 +1 @@
+# Example PDM configuration file.