[Proposal] Random Unification

Update implementation link

Update current example

Correctly gets a number within the bounds

Fixes some typos

Update implementation text

Update proposal to match mailing list discussions

Use `SecRandomCopyBytes` for older macOS versions

Update to reflect mailing list

Rename pick to sampling

Clarify a lot of discussions

Use focus instead of scope

Final remark for T.random

Fix some typos

Prefer UInt over UInt64

Comment more on design

Author: Azoy