Improve detection of circular includes

[xoorath]

Currently Source/Renderer.cpp has a hard coded include depth limit of 30 (see k_maxIncludeDepth). This is to detect/handle circular includes with a limit that's high and unlikely limit to occur in real uses of esd.

This can be improved by detecting circular includes prior to rendering anything by building some kind of include graph with that detection.

Goals for this improvement:

• No coded-in limit to the depth of includes.
• Detection occurs before rendering / before the output file or any temporary files are created or modified.
• Detection indicates to the user how to fix their problem / what files are a part of the circular dependency.