meta/new-web: release announcements as data

... instead of only git meta-data attached to tags.
raco exe: normalize runtime-file paths

Normalization is needed to ensure that `raco dist` doesn't generate
longer paths (by converting a "/" to "\\", for example) in its
path manipulations.
raco dist: preserve relative location of runtime files only within a package

Previously, relative locations were preserved for all files with the same
root, but that tends to keep too much information about the original
filesystem layout, especially when runtime files are pulled both from
the installation and a user-specific area. Since packages can be installed
at different relative locations, it makes sense to preserve relative
locations only up to package boundaries.
racket/draw Cocoa: fix dylib list as needed for `raco exe`