In addition to the old `*.lessimport` and `*.import.less` mechanisms for
telling the `less` package that a file isn't a root, you can also put it
in an `import` subdirectory or pass `{isImport: true}` to
`api.addFiles`. We no longer will need to rename every less file when we
upgrade.
Next commit will revert the changes to examples and docs.
bdf1968ceb