- remove auto-stored session "@" on restore
- minor help update

This reverts commit cf388649b9.

- replace bools for internal non-persistent binary states with an uchar
- do not store path to session, derive from config path in tmp buffer
- program option to load session is not `-s`
- remove auto-stored session "@" on restore
- minor help update

Remove extra static string.

* Initial commit of sessions implementation

* Reduce code duplication

* Move load session to program flag -e

* Fix context initialization problem when loading session

* Add pinned directory to session and reduce session file size

* Make load_session print an error if exists and few minor adjustments

* Refactor session's file structure

* Initialize required structures in load_session before loading

* Add load session dynamically, restore last session, and extra fixes

* Fix indentation

* Add sessions documentation to man page

* Update fish completions with sessions and make some improvements

* Move to single keybinding session management and add help info

* ESC when asked to insert session name behaves better

* Add sessions completion for bash

* Remove pinned dir from session and minor code refactors

This reverts commit e226e8c889.

This is a conveninece for nav-as-you-type mode.
With this program option, on pressing ^P, the filter is  executed as cmd.