Show-BuildGraph

Requirements:
- Invoke-Build command is available for calls
- Internet connection for using online viz-standalone.js
- or viz-standalone.js in the path, https://github.com/mdaines/viz.js
- or, when -Dot, dot in $env:Graphviz or in the path, http://graphviz.org/

The script calls Invoke-Build to get the build tasks, makes the DOT graph,
and uses either Viz.js or dot in order to convert the graph for show.

Tasks without code are shown as ovals, conditional and incremental tasks as
notes, other tasks as boxes. Safe references are shown as dotted edges,
normal references as solid edges. Job numbers are not shown by default.

EXAMPLES

# Make and show HTML using viz-standalone.js (local or online)
Show-BuildGraph

# Make and show SVG using dot
Show-BuildGraph -Dot

# Make Build.png with job numbers and top to bottom edges
Show-BuildGraph -Dot -Number -NoShow -Code "" -Output Build.png