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 for a GANNT Chart

{{#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

Flow Chart

{{#mermaid:graph TD
A[Christmas] -->|Get money| B(Go shopping)
B --> C{Let me think}
C -->|One| D[Laptop]
C -->|Two| E[iPhone]
C -->|Three| F[fa:fa-car Car]
}}

produces

Sequence Diagram

{{#mermaid:sequenceDiagram
	Alice->>+John: Hello John, how are you?
	Alice->>+John: John, can you hear me?
	John-->>-Alice: Hi Alice, I can hear you!
	John-->>-Alice: I feel great!
}}

produces

Class Diagram

{{#mermaid:classDiagram
	Animal <|-- Duck
	Animal <|-- Fish
	Animal <|-- Zebra
	Animal : +int age
	Animal : +String gender
	Animal: +isMammal()
	Animal: +mate()
	class Duck{
		+String beakColor
		+swim()
		+quack()
	}
	class Fish{
		-int sizeInFeet
		-canEat()
	}
	class Zebra{
		+bool is_wild
		+run()
	}
}}

produces