Refac generated documentation

Closes #183 (closed) and fixed the xtask gen-doc that was not compiling anymore.

cargo xtask gen-doc will now generate the rust autogenerated documentation (the full (and bloated) documentation is necessary for Substrate pallets calls). The docs/api/runtime-calls.md will be generated with reference to the rust autogenerated documentation based on the BASE_URL variable.

The only thing left to do is to decide where to store the rust autogenerated documentation. Then, a CI with the necessary server permissions can simply run:

BASE_URL="https://url/to/endpoint" cargo xtask gen-doc
rsync -a ./docs/api/doc user@server:/path/to/endpoint/

xtask/res/templates/runtime-calls-category.md

@@ -23,8 +23,7 @@ Taking {{ call.weight }} % of a block.
 ```
 </details>
 
-{# replace markdown sytax in documentation breaking the final result #}
-{{ call.documentation | replace(from="# WARNING:", to="WARNING:") | replace(from="## Complexity", to="**Complexity**") }}
+See [Pallet::{{ call.name }}](./doc/{{ pallet.type_name }}/pallet/struct.Pallet.html#method.{{ call.name }} )
 
 {% endfor -%}
 {% endfor -%}