Persist a generalized history of visited URL in history_file and try to keep it in sync during telescope usage and shutdown.

found on freebsd: closing a tab caused the message "event_pending: event has no event_base set" to be print.

load_url needs to know when a tab passes from lazy to not lazy to correctly saves the scrolling position (see follow-up commit.)

Save the offset to the first and current line of the buffers and restore it when the page is loaded. This restores almost the exact viewport: we save the offset of the *real* line in the document, but they get wrapped before being displayed, so the actual restored position may be slightly above from the original one (think of a long paragraph that gets wrapped over multiple visual lines.) In practice, this isn't a drawback but only an improvement over the current behaviour. In the future we could save also the offset *inside* the line, to restore the exact position, but that felt unnecessary for now. Persisting the postion on the session file ensures that even when re-opening telescope the scroll position is correct. There are some very active pages, such as antenna or other aggregator, where this feature doesn't really work well if you re-open the page after a while, since new links are available, but otherwise is a god sent! See also github issue #1

a missing ui_schedule_redraw on unkill_tab means that the tabbar is not rendered when calling tab-undo-close when there is only one tab.

This changes the last argument of load_url to be a `mode' bitmap instead of a boolean ``nohist''. LU_MODE_NOHIST is the old 1, LU_MODE_NONE is provided just for readability and the new LU_MODE_NOCACHE allows to bypass the caching when loading a page. Telescope only uses the cache when: - re-opens a closed tab - navigates backward and forward in the history All other situations result in the usual network request.

The other option, less intrusive, would be to send the killed tabs in reverse order, but it'd seems strange when looking at the session file otherwise. So, add a `append' flag to kill_tab to optionally append the killed tab instead of pre-pending it.

free_tab now operates exclusively on the killed tabs list, so don't mention the current_tab.

when freeing a tab we have to release also its history.

Save closed tabs to a "killed tabs" queue, for up to a max of "max-killed-tabs", and allow to re-open them. Keep the tab history but not its content. This integrates nicely with the session file, just add the "killed" flag as alias for TAB_KILLED and put it in the ktabshead queue upon initalization. It's thus possible to re-open closed tabs even after telescope has been closed, and tabs keeps their history! Add a new cmd, cmd_tab_undo_close, to try to re-open the most recently closed tab and bind it to `u'. While here, add a TODO for the tab history memory leak.

The session file is now overloaded with the history info, that means that upon startup telescope can repopulate each tab history! The price to pay is that one can't start an old telescope with a new session file, otherwise will get a lot of fancy '<' and '>' tabs...

it's cleaner to just toggle the lazy bit in switch_to_tab instead of pushing that complexity in load_url. While there also try to simplify the function and its documentation from unnecessary checks and extra verbosity. This also fixes a bug where Telescope ended up pushing the url on the history *twice* at startup.