Something that'd make life easier for sharing code like this would be GitHub; it'd also mean you wouldn't need anyone to worry about mentally filtering out object files or generated executables. But that's completely off topic.
It's nice to see somewhat consistent formatting. Definitely a great start.
Only thing I can really see is the use of the 'TYPE' enumeration in 'entity.h'. You've tied the entity class quite heavily to it but you've kept the enumeration outside of the class. I'd recommend putting the definition of the enumeration as a public member of the class. It means if you copied the class you'd not accidently forget about including it.
EDIT: Also, Bjarne Stroustrup recommends making base classes take care of themselves. You've provided an interface for tracking member changes but you've also made all the members 'protected' giving derived classes access anyway. Make them private and force access through through functions; at least that way you can enforce value ranges, etc in an easier fashion.