(feat): Unpack extensions into complex function types #8

The more in-depth we use extensions, the more likely is is that we need custom extensions. New `UnpackExtensions` function in the high package makes this easy. Low level models have been updated to support feature fully and docs added in README and examples as well.

Signed-off-by: Dave Shanley <dave@quobix.com>

datamodel/low/v3/parameter_test.go

@@ -86,6 +86,7 @@ content:
 
 	ext := n.FindExtension("x-family-love").Value
 	assert.Equal(t, "strong", ext)
+	assert.Len(t, n.GetExtensions(), 1)
 }
 
 func TestParameter_Build_Success_Examples(t *testing.T) {