Feature proposal: cell output export

Hello, I am glad to see the work which has been done here!

I am using a lot of notebooks, and I would like to automate them, and get specific cells output. I think the easier way to do so would be to run a notebook using dotnet-repl, identify a cell, and get its raw output as a file. I have a crude pipeline, and I am looking for a way to improve it, either with existing nugets, or by suggesting a feature.

The problems

1: a way to give a name or id to a cell I am talking about a user defined name, not an automatic one like the cell number.

Using ipynb format, we can have a first line comment such as #id:myFinalOutput, which can be parsed later from the cell source.
Using trx format, the first line of the cell is used to create a parameter testName="Cell X: first_line_of_the_cell".
Maybe a magic command would be better?

2: a way to get a raw output of the cell

Using ipynb format, the output looks like this:

"outputs": [
{
 "name": "stdout",
 "output_type": "stream",
 "text": [
  "0\r\n",
  "1\r\n",
  "2\r\n",
  "3\r\n"
 ]
}
]

Using trx format, the output looks like this;
```
  <Output>
    <StdOut>0
1
2
3</StdOut>
  </Output>
```
It's possible to parse the files. But I think it would be better if dotnet-repl outputs directly the raw output to a a file.

Proposal for one output

The notebook

#!cellid myFinalOutput
Console.WriteLine("Hello World");

The command line dotnet repl --run /path/to/notebook.ipynb --output-path /path/to/output.txt --cellid myFinalOutput

The output (output.txt) Hello World

As the output is raw, it could also be some html.

Proposal for several outputs

Managing several outputs for several cells.

The notebook

#!cellid myIntermediaryOutput
2 + 2

#!cellid myFinalOutput
Console.WriteLine("Hello World");

The command line dotnet repl --run /path/to/notebook.ipynb --output-path /path/to/folder --cellid myIntermediaryOutput,myFinalOutput

myIntermediaryOutput.txt 4
myFinalOutput.txt Hello World

jonsequitur / dotnet-repl