Put duplicated code inside the transaction, which is used by both tests and raster_to_gtiff
Removed <filesystem> header, reimplemented one of its utilities for file checking
Code style changes
Replaced .data() with .c_str() for std::string
Updated README to show how to build both GDAL and PROJ inside the build folder and how to link them to the sandbox
Implemented simple GTiff file parser to test sandboxed part of code on a real data, added unit tests.
Need to improve the CMake file to make it work without specifying the absolute paths to libraries.
