Adding a new command for evaluating in line and instructions for other kernels

[WhiteBlackGoose]

Closes #74

Jupyter supports any kernel, not just python's. That makes it usable for other languages, such as C# and F#. To use them, you have to make its output mimetype text/plain, that's where we need MagmaEvaluateArgument. Example of this command:

:MagmaEvaluateArgument a=5;

That will assign 5 to variable a in current context.

I also added an example of vim commands to add for kernel initialization. That makes it easier to use with, say, telescope. And by default it overwrites mimetype to text/plain for C# and F#.

Note that I merged @LoipesMas into my fork to make things easier for myself.

[WhiteBlackGoose]

Gonna change the branch