Mermaid

Editing a complex diagram and integrating that into your documentation shouldn't be hard. The Mermaid library makes diagrams of all types accessible through simple markup. See examples

Mermaid
flow diagram
Image shows:	flow diagram
Summary
Title:	Mermaid
Description:	A diagramming language. Make diagrams and flowcharts for documentation, easier. With simple syntax, create sophisticated diagrams, flowcharts, GANTT Charts etc.
More
Notes:	Use the online editor to create your diagram
Example:	See the example diagram at Sales Cycle

Code like this

{{#mermaid:gantt
	title A Gantt Diagram
	dateFormat  YYYY-MM-DD
	section Section
	A task           :a1, 2014-01-01, 30d
	Another task     :after a1  , 20d
	section Another
	Task in sec      :2014-01-12  , 12d
	another task      : 24d
}}

produces