Use title of man page instead of function name

[etiennebacher]

The name of the function is already shown in the sidebar anyway. @vincentarelbundock what do you think?

Before PR:

After PR:

[vincentarelbundock]

Ooh, I muuuuuuuch prefer to display the function name. For sure. The title can sometimes be very long, and users looking for documentation will typically refer to function name, just as they would when typing ?render_docs. In R, help and docs are accessed by function names, so we should be consistent.

[vincentarelbundock]

Oooh, sorry, you mean as the H1 of the page, not the sidebar! I have much less feelings about those. I feel that it's still useful to have the function name up top, but am close to indifference on this

[etiennebacher]

In R, help and docs are accessed by function names, so we should be consistent.

They are accessed by function names, just as one would use the search bar or would look for the name in the sidebar on the website. However, in the R docs the title is displayed in big and the function name in small so it would actually be more consistent to display the title on the website