Fix `‘unique_ptr’ was not declared in this scope`

[Ryan-M-Smith]

When compiling EasyBMP, the following error is thrown on line 771 of EasyBMP.cpp:

error: ‘unique_ptr’ was not declared in this scope

For reference, here is line 771:

unique_ptr<ebmpBYTE> Buffer(new ebmpBYTE[BufferSize]);

This error is thrown because <memory> is not included in EasyBMP.h, as explained in #1, so we can't use std::unique_ptr. This pull request fixes that issue by including <memory> in EasyBMP.h.