Reference doc of all Aztec macros

[jzaki]

User Story - As a developer new to Aztec, I would like an understanding of what goes on in macros (eg "private"), so that I can have confidence in writing privacy preserving applications.

There are some references to different macros around the docs, but a search doesn't yield a doc that readily lists them all, defining what they do.

Task - Create a reference doc that generally explains Aztec macros, and defines each one.

[jzaki]

Summary of function level macros can be seen in VSCode via Ctrl+K then Ctrl+2 (fold to depth 2), then Ctrl+K then Ctrl+J (to unfold)

Related https://github.com/AztecProtocol/aztec-packages/issues/5162

[critesjosh]

Related: https://github.com/AztecProtocol/dev-rel/issues/200 <- this one is an explainer vs a reference