Change include path to forward slash, friend class declaration before public access modifier for datastore

Conflicts:
	You-DataStore/TransactionManager.h
Add const modifier to parameters that are not supposed to be modified
Remove redundant constructor and destructor declaration
Add unit test for post method
Update documentation
Implement post
Modify documentation
Add test for put method
Rename KeyPairValue to KeyValuePair
Add constants for unit test
Add another test for put method
Implement put
Modify test for get
Add pvt methods for serialization, minor modification to typedefs
Implement deserialize and get method
Add test for get method for non-existent task id
Modify get to pass unit test
Add basic test for erase
Implement erase
Add more test for erase