Add include-it-raw literate command

[HLWeil]

This pull request addresses issue #611.

The idea is to have a way to include results of snippets not formatted as fsi output but just as plain text. This allows for formatting them as html, e.g. as charts, as can be seen here. In the example, this was done by using a custom evalutator, which is not feasible with the fsdocs tool.

Therefore I added a new literate command include-it-raw, which evaluates the snippet, but then inserts is as plain text. As a small example I used this to embed a html table from a jagged array:

The code in the Evaluator.fs got a little bit messy, as strings are formatted surrounded by "s, which show up in the final document and might even hinder the correct html formatting. I remove them in the Evaluator.Format method but maybe you have a better place or idea?

[cartermp]

@HLWeil could you look into adding a test here? https://github.com/fsprojects/FSharp.Formatting/blob/master/tests/FSharp.Literate.Tests/EvalTests.fs

[HLWeil]

Sure thing! Something like this?

[cartermp]

Thanks, this is a good addition. I take it this lets you also output the HTML string for a chart yes?

[cartermp]

Will merge, as this is a good change that does what you're after here.