CUPS plugin (#5188)

* Implement a CUPS collector plugin

* Compile cups.plugin only if enabled

* Fix build with CFLAGS

-O1 -ggdb -Wall -Wextra -Wformat-signedness -fstack-protector-all
-DNETDATA_INTERNAL_CHECKS=1 -D_FORTIFY_SOURCE=2 -DNETDATA_VERIFY_LOCKS=1

* cups.plugin check for all used functions

* Use cups-config to configure cups compiler flags

* Do not quit if cups-config is not installed

* Fix compiler warning

collectors/cups.plugin/cups_plugin.c:359:27:
warning: format '%d' expects argument of type 'int',
but argument 6 has type 'unsigned int' [-Wformat=]

* Add cups.plugin to toc and overview documentation

* cups.plugin fix plugin doc layout

* cups.plugin: Add prerequisites doc

* cups.plugin: Fix error if cups is not installed

1 files changed, 1 insertions, 0 deletions

diff --git a/collectors/plugins.d/README.md b/collectors/plugins.d/README.md
index 53dc4411a4..6f5294cd6a 100644
--- a/collectors/plugins.d/README.md
+++ b/collectors/plugins.d/README.md
@@ -9,6 +9,7 @@ plugin|language|O/S|description
 :---:|:---:|:---:|:---
 [apps.plugin](../apps.plugin/)|`C`|linux, freebsd|monitors the whole process tree on Linux and FreeBSD and breaks down system resource usage by **process**, **user** and **user group**.
 [charts.d.plugin](../charts.d.plugin/)|`BASH`|all|a **plugin orchestrator** for data collection modules written in `BASH` v4+.
+[cups.plugin](../cups.plugin/)|`C`|all|monitors **CUPS**
 [fping.plugin](../fping.plugin/)|`C`|all|measures network latency, jitter and packet loss between the monitored node and any number of remote network end points.
 [freeipmi.plugin](../freeipmi.plugin/)|`C`|linux|collects metrics from enterprise hardware sensors, on Linux servers.
 [node.d.plugin](../node.d.plugin/)|`node.js`|all|a **plugin orchestrator** for data collection modules written in `node.js`.