Sequential numbering for 0012, 0025, and 0030

[1ucian0]

The RFC process defines a sequential numbering. So:

• renamed: 0012-unify-pulse-commands-and-instructions.md -> 0008-unify-pulse-commands-and-instructions.md
• renamed: 0025-interface-for-circuit-operations.md -> 0009-interface-for-circuit-operations.md
• renamed: 0030-simple-classical-representations.md -> 0010-simple-classical-representations.md

[jakelishman]

"Sequential" doesn't necessarily require "consecutive" - I think it's better to keep the relation of an RFC to its historical context via the PR review.

[1ucian0]

Yeap. I should had said consecutive. Alternatively, we could link to the PR in the README table? Following the discussion in #39 (comment), the table in README file includes a column pointing to the original PR and other references.