CIP-0030 | A few small fixes

[Ryun1]

See these few small formatting fixes.

Changes:

1. Changed old style links that pointed to CIP-0005.md, these would require a short redirect because of past change to CIP markdown file naming.
2. Added javascript language indicators for code snippet data types and error codes.
3. Added missing APIError for api.getExtensions().
4. Fixed incorrect reference to cardano.{walletName}.extensions which was removed during development of CIP-0030 | Upgrade to latest format & propose version / extension scheme #446. Replaced with correct reference to api.getExtensions().
5. Fixed highlighting for references to APIError, to all be APIError and not APIError.
6. A couple small spelling fixes.

Motivation:

1. Just more convenient to follow direct links.
2. Will rendered the snippets with syntax highlighting which improves readability.
3. This seems like an oversight and not intentional design.

[rphair]

Looks good to me & it's especially helpful to have that update from the extensions field to method: that could cause some real problems for new arrivals to the standard (we tend to miss things like that when we've been working with something for a while).

Also tagging a few more contributors to the CIP in case they might add anything else (apologies if I've missed anyone): @rooooooooob @alessandrokonrad @refi93 @vsubhuman

[Crypto2099]

Simple, mostly cosmetic and housekeeping changes, see no reason not to merge as-is.