Add new z key in man page

Fix case.

Implement toggle of process list display

Adapt to psutil 2.0.0 API.

Fixed psutil 0.5.x support on Windows

Don't know why adding "None" as second default helps.

API changed.
https://psutil.googlecode.com/hg/HISTORY

Tested with 0.5.1, 1.2.1, 2.0.0

Parsing and displaying the process list takes a sometimes significant
amount of resources.  Since there is already a mechanism in place to run
glances with the process list disabled, it was easy to add a toggle to
the __catchKey function.

Fix lintian warning from debian packaging

Distinguish between mandatory and optional dependencies.
Linux: Add Void Linux https://github.com/voidlinux/xbps-packages/tree/master/srcpkgs/glances
FreeBSD: Add installation instructions for pkgng.

Add steal time to the global CPU/per-CPU time accounting.
Add steal limits, alerts, and log support.
Update help screen.

Based on PR #309 by @pcn