This PR makes it possible to create a diagram from a plain *diagram.Options struct.

The motivation behind this PR is that one cannot set the Name field of a diagram's options.
While the preferred way of creating a diagram seems to be passing Option functions that override the default ones, allowing the user to simply pass the object is much more flexible.
It is also not possible to create a Name function that would set that field, because the diagram package already contains such a function that sets a node's name.

Maybe all node-related functions should be moved to a separate package to avoid such collisions?

This addresses https://github.com/blushft/go-diagrams/issues/12

For groups, this strips the label if it's empty. For nodes, this uses empty string as the default label which also results in the label attribute being stripped if empty.

This is necessary because otherwise the default values don't lead to valid graphviz code.

Hello there,

first of all thanks a lot for this library. :)

tl;dr: i've found issues with the default labels for groups and prepared a corresponding PR.

When trying it out, I found some issues with default labels, that can cause problems for newcomers especially if they don't know anything about graphviz.

The default label for a group is the empty string. When rendered, it produces label=; which to graphviz is a syntax error. So, in order to produce a valid graph, at least the diagram.Label option is needed, as far as I see it. If I'm not mistaken, this could be fixed by adding a call to trimAttrs here: https://github.com/blushft/go-diagrams/blob/master/diagram/options.go#L39

d, err := diagram.New(
	diagram.Label("TEST"),
)

The default label for a node is "node". This is a reserved keyword in graphviz and when left unescaped causes problems. Since graphviz has logic for automatically labelling nodes, I would suggest using empty string here, as well and letting graphviz set the label. The alternative would be something like "\"node\"" which doesn't feel right to me. But feel free to suggest that on the PR if you see it differently.

I added an icon for https://screwdriver.cd as ci tool.

The tool's name has cd in it, but I've included it in the ci dir because I think the role of this tool is similar to that of Jenkins.

When I am using dot to produce JPG or PNG file I receive such a Warning:

dot -Tjpg app.dot > ./1.jpg
 Warning: #@D3436 is not a known color.

Note that all over other places code has #2D3436 not #@D3436 . https://github.com/blushft/go-diagrams/blob/master/diagram/node.go#L140

Use as label first 8 bytes from SHA1 digest in label and I think that I found some escape problem:

        vkhkhzkc [ fixedsize=true, fontcolor="#2D3436", fontname="Sans-Serif", fontsize=13, height=2.1999999999999997, image="assets/gcp/database/sql.png", imagescale=true, label="2822b7f1...", labelloc=b, shape=none, style=rounded, width=1.4 ];
        xnxdisdb [ fixedsize=true, fontcolor="#2D3436", fontname="Sans-Serif", fontsize=13, height=2.1999999999999997, image="assets/gcp/database/sql.png", imagescale=true, label=ca20af73..., labelloc=b, shape=none, style=rounded, width=1.4 ];

Look like label label=ca20af73... sounds like string is't escape properly by go-diagrams.

As result cath an error in dot processing:

Error: diagram.dot: syntax error in line 30 near '.'

When running a go-diagram more then once, the Render method errors with the following message:

mkdir go-diagrams: file exists

Ideally Render supports the option to overwrite the dot file in the go-diagrams directory.