Mastopod/ActivityPods compatibility report

# Context
Handling feature #27 was the occasion to try to access multiple federated tools from mastopod Actor's page (`https://mastopod.com/actor/@@`) and discover that in there was compatibility issues.

This issue is intended as a working document to inventory the tested tools, identify and qualify compatibility issues when they were found.

# Inventory

| Tool | Category | Expected object type | Actual object type | Compatibility |
| --- | --- | --- | --- | --- |
[Mastodon](https://joinmastodon.org/) | Social | [as:Note](https://www.w3.org/ns/activitystreams#Note) | [as:Note](https://www.w3.org/ns/activitystreams#Note) | No issue |
[Peertube ](https://joinpeertube.org/en)| Media sharing | [as:Video](https://www.w3.org/ns/activitystreams#Video) | [as:Video](https://www.w3.org/ns/activitystreams#Video) | No issue |
[Pixelfed ](https://pixelfed.org/)| Media sharing | [as:Image](https://www.w3.org/ns/activitystreams#Image) | Unknown | Blocking issues |
[Castopod ](https://castopod.org/)| Media sharing | [as:Audio](https://www.w3.org/ns/activitystreams#Audio) | [as:Note](https://www.w3.org/ns/activitystreams#Note) | Blocking issues |
[Funkwhale ](https://www.funkwhale.audio/)| Media sharing | [as:Audio](https://www.w3.org/ns/activitystreams#Audio) | Unknown | Blocking issues |
[WriteFreely ](https://writefreely.org/)| Blog and publishing | [as:Article](https://www.w3.org/ns/activitystreams#Article) | [as:Article](https://www.w3.org/ns/activitystreams#Article) | Blocking issues |
[Plume ](https://joinplu.me/)| Blog and publishing | [as:Article](https://www.w3.org/ns/activitystreams#Article) | [as:Article](https://www.w3.org/ns/activitystreams#Article) | Non blocking issues |
[Mobilzon](https://mobilizon.fr/)| Events | [as:Events](https://www.w3.org/ns/activitystreams#Events) | [as:Events](https://www.w3.org/ns/activitystreams#Events) | Non blocking issues |

# Issues

## Pixelfed

1. Outbox's content of an actor cannot be publicly accessed
2. When following a pixelfed actor from mastopod.com, a 401 occurs when pixelfed posts to the actor's inbox

## Castopod

## Funkwhale

## WriteFreely

## Plume

## Mobilizon