Restructure API page

[carme-hp]

Fixes #715

[carme-hp]

I have restructured the pages using bullet points + bold letters

The design does not look particularly appealing to me. I also tested alternatives:

• bullet points (not bold)

• blockquote

• table

• table (not bold)

Let me know which of the options above you prefer. Feel free to suggest another option.

[MakisH]

Thanks for the updates! Looks good overall.

I don't mind the boldface, but without would also be fine.

I would not use a blockquote (semantically different). I would also not use a table with one column, as shown in the alternatives.

I guess a table with a title column is not supported in Markdown / this Markdown flavor. But the current style is fine (for me) anyway.

[MakisH]

I applied a few more changes directly:

• Added links to various pages of api.precice.org, for main and develop.
• Removed the source documentation page, added a redirect to the API page, and updated URLs.
• Added usage examples, as motivated in Update the C++ API location / URLs #836.
• For sections where usage was not trivial, or there is no source documentation, I skipped the respective field.

The page now looks like this:

@fsimonis any further suggestions?

[MakisH]

From my side, this is ready. Maybe @fsimonis has more points here.