julia

c124bf92 - docs: Add headers for easier Core, Base and stdlib reference (#55311)

docs: Add headers for easier Core, Base and stdlib reference (#55311) This adds one new section (h2) and a nested subsection (h3) to the landing page of the Julia documentation website and associated PDF file. The new section provides a quick overview of the differences between `Core`, `Base` and the standard library, as well as a list of links to standard library packages. The list of standard library packages is thus duplicated in the website sidebar, but I don't think this is an issue because the sidebar is primarily intended for navigation, whereas this list is primarily intended to be used for referencing purposes. Partially addresses #28712, although I don't provide short descriptions of each standard library package. I think the appropriate place for that would be in module-level docstrings of the packages themselves, which are not currently available. --------- Co-authored-by: Viral B. Shah <viral@juliacomputing.com> (cherry picked from commit abb104c56f5a43e6511bb5cfa1a6586a4fc8cd46)