* Use SPDX identifier in header files
* Use SPDX identifier in rest of source files
* Fix usage of SPDX for files with 2 licenses
* Add global license file
* Fix compilation
- reimplement binaryToString:
- it now accepts a Slice and nothing else
- it does not return a std::string but instead a proxy object that implements
operator<< (this should be more efficient, as we do not need to touch the
heap in most cases)
- addapt unit tests
- replace all occurences with the new API