Erase method

[alvarofpp]

Implement method of erase and test.

Here are some drafts:

// cdf.h

template< class InputIterator >
bool erase ( InputIterator _first, InputIterator _last );

// DataFrame.cpp

template< class InputIterator >
bool cdf::DataFrame::erase ( InputIterator _first, InputIterator _last )
{
	bool result = true;
	while (_first != _last)
	{
		if (!drop(*_first))
			result = false;
		++_first;
	}

	return result;
}