CIP-0054 | Fix API headers for markdown portability

[SmaugPool]

\< is supported by GitHub to escape HTML but not part of Markdown spec and not supported by showdown, breaking CIP-0054 rendering on https://cips.cardano.org/:

By escaping instead the opening angle bracket with <, both GitHub and showdown rendering work correctly:

GitHub rendering:
https:/SmaugPool/CIPs/tree/cip54-fix-rendering/CIP-0054

FYI: @kieransimkin

[rphair]

@SmaugPool can you anticipate any problems with Showdown rendering if these API headers were more properly typeset as code? https://gist.github.com/rphair/d206e385ef694396841f765a6dd27696

[rphair]

p.s. @SmaugPool @Ryun1 this is also an issue for CIP-0030 (I just checked all merged CIP README's [grep '^#' CIPs/*/README.md] and only found this additional one with code in the headers) so I'm going to commit #591 (review) so we can test it a bit more on the smaller & less popular CIP before maybe updating the CIP-0030 API headers also in this PR.

[SmaugPool]

@SmaugPool can you anticipate any problems with Showdown rendering if these API headers were more properly typeset as code? https://gist.github.com/rphair/d206e385ef694396841f765a6dd27696

Inline code in the headers also solves the issue but it's displayed differently, and I didn't want to change the author formatting intention. I guess it's also an acceptable solution though if preferred.

[rphair]

OK @SmaugPool @Ryun1 let's put this through then (unless @kieransimkin has any objections) and after it's agreed upon I'll submit a PR to update CIP-0030 the same way... this may require some care because of potential merge conflicts with pending CIP-0030 updates, so I think we should keep the 2 sets of changes separate.