High-level documentation of the interaction between tools in the decompilation pipeline

This issue tracks the addition of high-level documentation, which describes the interaction between the various tools of the decompilation pipeline, what input they take (i.e. which input formats, produced by which tools) and what output they produce.

From my current understanding of the RetDec decompilation pipeline, this could be described with the following graph. For those with better understanding, feel free to update the graph to make it more accurate, and provide additional comments on the interaction between these tools. Once a good high-level documentation has been produced, it may be added as Markdown files to some directory, perhaps `doc`? Or `design`?

DOT file at: https://gist.github.com/mewmew/bf74e6fc0e96ab67576982baacc17937


(Note, in the above illustration, blue boxes represent tools, light green circles input and output formats, and darker green circles meta input and output formats. A meta input and output format is a set of formats (e.g. "binary" is ELF or PE or raw, etc).