Second large revision of concept exercises

[oxe-i]

Another revision on concepts and concept exercises:

1. Includes message for tests in Color Palette.
2. Modifies test messages in Bird Watcher to return the values in each byte.
3. Clarifies instructions in Secrets.
4. Adds some missing links.
5. Clarifies instructions in Mixed Juices, to explain about how chars may be handled in task.
6. Adds General hints to each task's hints in various concepts.

May be merged with [no important files changed]

This PR is the result of observations in this topic: https://forum.exercism.org/t/the-x86-64-assembly-syllabus-is-live/19777/27

[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

If this PR does not affect the result of the test (or, for example, adds an edge case that is not worth rerunning all tests for), please add the following to the merge-commit message which will stops student's tests from re-running. Please copy-paste to avoid typos.

[no important files changed]

For more information, refer to the documentation. If you are unsure whether to add the message or not, please ping @exercism/maintainers-admin in a comment. Thank you!

[kotp]

Overall looks good. Some "grammer" things.

[kotp]

Should the .rodata and .data words be code formatted?

[kotp]

There were others, this was an example. Not a high priority, though, for sure.