Introduce Overview HTML page and time-based navigation links

[iher1]

Hi,
another idea to make it easier to consume many conversations and very huge chats would be:

• generate an index.html page which provides links to the specific chat entry pages
• when working with the --size parameter: have some sort of index at the beginning of each html page to quickly jump to
  • a certain subpage, like page 1 2 3 4 5 6 ...
  • jump to the first chat of a specific date, e.g. have links per year: 2020 2021 2022 2023

Regards
iheri1

[KnugiHK]

Continue on #101.