Add stmt.paramData() and a test
Begin stmt.putData() work

Fix ParamDataOperation::parameter_ not being initialised
Move some buffer code into buffer.cpp
Implement stmt.putData()

Change Parameter::GetValue() to be a settable accessor
Change Parameter::Indicator() to return a non-const reference to the
value rather than a pointer
Merge pull request #2 from lee-houghton/DataAtExecution

Data at execution