Show Tool Bar on Mouse Hover

It's more like a sharing rather than an issue.

Just adding following snippet to `~/.atom/styles.less`

```less
@toolBarSizeHidden: 1px;
@barSizeWhenIcon12px: 30px;
@barSizeWhenIcon16px: 38px;
@barSizeWhenIcon24px: 54px;
@barSizeWhenIcon32px: 70px;
// NOTE barSize = 2*iconSize + 6px
@transitionTime: 1000ms;

.tool-bar-top, .tool-bar-bottom{
height: @toolBarSizeHidden;
transition: height @transitionTime;
&:hover {
height: @barSizeWhenIcon24px;
transition: height @transitionTime;
}
}
.tool-bar-left, .tool-bar-right {
width: @toolBarSizeHidden;
transition: width @transitionTime;
&:hover {
width: @barSizeWhenIcon24px;
transition: width @transitionTime;
}
}
```
You can switch to different variables according to your icon size.

Now you can show tool-bar by just moving your mouse which is easier for me.

Start with the provided ~/.atom/styles.less snippet and its .tool-bar-* selectors; the issue does not identify a repository file or test. Clarify whether the goal is to document this customization or add hover behavior to the package, then define acceptance criteria before implementation.

Written by the indexing model from the issue text.