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 *
Implemented move_to_beginning_of_next(), move_to_end_of_next(),
move_to_beginning_of_previous() and move_to_end_of_previous() functions
for more correct word jumping than the move_to_xxx_span() methods that
were previously used.
