* WIP - Substruct Library Serialization
* Add serialization to SubstructLibrary
* Add SubstructLibraryDefs
This holds the definition of whether the substruct
library is serializable
* Wrap serialization in python
* Remove .h file, add .h.in file
* Configure header file into source dir
* Use RDConfig.h to configure serialization
* Move serialization code to seperate header file
* Fixes for review comments
* Removes some code redundancy
* Make pickling mols less memory intensive
* Check if molholders come back as the right types
