SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
I totally forgot about the C++ basics here. There are three distinct
types: "char", "signed char" and "unsigned char". Whether "char" is
signed or unsigned is implementation specific.
