[JumpTo] Added cursor navigation

Previously you had to know precisely where to put a new line:

    $editor->addAfter($add, $after);

The problem arises when you have a line which is present many times. This
commit provides the solution: cursor navigation!

    $editor->jumpDownTo($to);
    $editor->jumpDownTo($to);
    $editor->addAfter($add);
    $editor->addBefore($add);

Autosaving and multi file holding have been dropped.
Merge branch 'feat/cursor'
[DocUsage] Updated README to be more library like

The layout of the README was based on an application one.
The Update includes a shorter introduction, a nearest installation
documentation and a longest usage example.

The Feature list has been dropped.
[DocUsage] Improved usage documentation

Created documentation with:

* use cases
* usage
Merge branch 'doc/usage'
[0.2.0] Updated CHANGELOG