ShowGraphviz: Derive various show methods from text/vnd.graphviz

The main API of ShowGraphviz.jl is @deriveall. Given a type that defines show on DOT language MIME typetext/vnd.graphviz, it defines show methods for various image types such as PNG, GIF, SVG, PDF, etc.

struct HelloWorld end

Base.show(io::IO, ::MIME"text/vnd.graphviz", ::HelloWorld) =
    print(io, "digraph G {Hello->World}")

using ShowGraphviz
ShowGraphviz.@deriveall HelloWorld

svg = sprint(show, "image/svg+xml", HelloWorld())
occursin("<svg", svg)

# output
true

All top level functions and types (but not modules) defined in ShowGraphviz are public API.

• ShowGraphviz.@derive type mimes...: Similar to @deriveall but only define the methods with specified mimes.
• ShowGraphviz.show(io, mime, x): show x as an image of MIME type mime using dot command line program.
• ShowGraphviz.setoption(io, option): Set command line option for dot program via IOContext.
• ShowGraphviz.addoption(io, option): Append option.
• ShowGraphviz.getoption(io): Get option.

• ShowGraphviz.DOT(source): a wrapper object that converts DOT source
• ShowGraphviz.dot"source": create DOT using a string macro
• ShowGraphviz.CONFIG.dot: dot command
• ShowGraphviz.CONFIG.dot_option: global dot command option