ptree/Value: Integerate Array container & functionality into Value

* Removal of several unnecessary files (general clean up of this
side project!)
Property Tree: General clean up on source files
Introduce unit testing with Google Test framework

* Introduce tests/ptree.cpp; most of the tests in examples/values.cpp
will be migrated here.
Relocate JsonCpp dep to third-party/common dir
.gitignore: Add third-party/common to ignore filter

* Remove third-party/common/rapidxml -- these were never intended to be
pushed to the repo; see https://sf.net/p/nomlib
tests/CMakeLists.txt: Copy DLLs to tests output dir (WindowsOS)