Add user option 'logos-hide-header-line'
Expand example for bar toggling and fix the code samples

The code I had before was not toggling the mode on/off, whereas that
is what we want to achieve.

Thanks to Lasse Lindner for reporting the problem with those functions
and for testing my proposed solution.  This was done via a private
channel and the information is shared with permission.
Simplify the example with org-indent-mode
Bump version to trigger rebuild in light of commit 3a63703
Acknowledge Edgar Vincent for commit 3a63703

The discussion took place on the mailing list:
Fix (cond ...) in `logos-narrow-dwim'
Rephrase some statements in the manual
Give more descriptive names to functions that set state
Make logos-page-delimiter function and variable public

This is because they may be used in custom code that is defined at the
user level.  We want them to be "public" to suggest that they are safe
to use: their behaviour is predictable, while any breaking changes
will be documented.
Remove some needless private function notation from the manual
Rename logos-focus-mode-hook for correctness

The 'logos-focus-mode-extra-functions' has the unfortunate connotation
of being an irregular hook, i.e. one that is called with arguments.
Whereas this one is a regular hook that passes no arguments to the
functions it calls.

Quoting from the Emacs Lisp Reference Manual:

       If the hook variable’s name does not end with ‘-hook’, that indicates
    it is probably an “abnormal hook”.  These differ from normal hooks in
    two ways: they can be called with one or more arguments, and their
    return values can be used in some way.  The hook’s documentation says
    how the functions are called and how their return values are used.  Any
    functions added to an abnormal hook must follow the hook’s calling
    convention.  By convention, abnormal hook names end in ‘-functions’.

To read the manual, evaluate:

    (info "(elisp) Hooks")
Tweak format of the manual's front matter
Add README.md to make it easier for all Git forges

Thanks to Dave Abrahams for asking me to put a video demo in the
README.  This inspired me to update this repository to be in the style
of the others I also maintain.

Dave's comment was made in issue 12 on the GitHub mirror:
Add link to video demo in the manual
Bump version to include commit 6ef7408
Fix typo in CHANGELOG heading