Rather than attempt to use standard C++ type names, create a namespace specifically for environment variable types and require vars to use a type from that namespace. This avoids the annoying collision between this `string` and `std::string`, and makes everything a bit more consistent. Rename the types a bit to be more appropriate for this context: boolean, uint8, and uint32, instead of bool, uint8_t, and uint32_t.
Mike Ash
f7745f2094