The changes are mostly converting old-style explicit iterator for loops
into ranged for statements. A number of for loops had already been
changed over, but local variables had been left behind instead of being
absorbed into the ranged for statement, so these have been cleaned up
too. A couple of minor improvements were made in areas already being
updated by the for loop changes to slightly simplify the code or to
avoid unnecessary conversions between `const char*` and `std::string`.