debug.md: typos and MarkDown style

[siebenschlaefer]

The section about log_i64_s calls $log_i32_u:
https://github.com/exercism/wasm/blob/main/exercises/shared/.docs/debug.md?plain=1#L50

The section about log_i64_u uses a parameter of type i32:
https://github.com/exercism/wasm/blob/main/exercises/shared/.docs/debug.md?plain=1#L62

The section about log_mem_as_i8 calls $log_mem_as_u8:
https://github.com/exercism/wasm/blob/main/exercises/shared/.docs/debug.md?plain=1#L126

The section about logging 32-bit floating point numbers uses log_mem_as_u64 in the heading and calls $log_mem_as_u64:
https://github.com/exercism/wasm/blob/main/exercises/shared/.docs/debug.md?plain=1#L241-L252

The section about mem_as_f64 calls $log_mem_as_u64:
https://github.com/exercism/wasm/blob/main/exercises/shared/.docs/debug.md?plain=1#L267

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Additional things we might want to change:

One sentence per line (as required by the Markdown Styleguide):
https://github.com/exercism/wasm/blob/main/exercises/shared/.docs/debug.md?plain=1#L3
https://github.com/exercism/wasm/blob/main/exercises/shared/.docs/debug.md?plain=1#L9
https://github.com/exercism/wasm/blob/main/exercises/shared/.docs/debug.md?plain=1#L17
https://github.com/exercism/wasm/blob/main/exercises/shared/.docs/debug.md?plain=1#L93
https://github.com/exercism/wasm/blob/main/exercises/shared/.docs/debug.md?plain=1#L95

The document should have exactly one level one heading (which will not be displayed on Exercism's website), everything else should be level 2 or greater (see Exercism's Markdown Styleguide.)

Maybe surround the function names in the headings with backticks.