Uniform links and `.md` file names to allow link checker to work without false flags

[alelom]

As highlighted in the link strategy (#84), we can uniform our file names to enable the powerful link checker ability. This is required to avoid false flags, as for example happens here: #83 (comment).

In a nutshell:

1. Rename all .md files that have whitespaces in their name. Replace them with underscores or dashes (do we have a preference @al-fisher ? I think we've used dashes in some of them).
2. Replace all links to those files so they keep working in the exposed website and that the link checker doesn't detects them as false flags. This can be simply done by shift-dragging the file you want to link into the text.

See this comment for a strategy to identify all links to be uniformed.

[al-fisher]

Think-your-dashes-convention-works-well.

[alelom]

We_dont_fancy_snake_case_anyways!