Release 5.0

[Tienisto]

Not expected to be released anytime soon. This is just a public note.

• Set timestamp: false as new default #292
• Require "Remove namespace in file name" and "Add locale in file name" specified in https://github.com/slang-i18n/slang/blob/main/slang/MIGRATION.md
• Rename _default to _main namespace
• Support booleans and numbers as i18n content #342