0.25 release planning.

[sunfishcode]

I'm planning to publish a 0.25 release soon, after

• Don't apply a mask on the flags in PermissionsExt. #256
• cap-primitives: Add read_link_contents and symlink_contents #252
• Fix some cargo doc warnings. #258
• Remove File::with_options. #259
• Minor formatting cleanups. #260
• Fix a few miscellaneous clippy lints. #261

[sunfishcode]

0.25 is now released.