Support multi-word mermaid commands

[slanzmich]

To support words (paths, arguments) containing whitespace,
shell-compatible quotes or a list of strings can be supplied.

This fixes issue #89 in a more robust way than #79.

[mgaitan]

@slanzmich isn't the same than directly add the extra params in the mermaid_params config?

mermaid_params = [...]

[slanzmich]

Users cannot add the -i / -o commands, because they depend on the current input file and the temporary directory.

It is however not a problem if users specify these parameters in their command, because they will be overwritten by the ones we append. I.e.

npx mmdc -i input_1.md -o output_1.png -i input_2.md -o output_2.png

will convert input_2.md to output_2.png.

[slanzmich]

Sorry, I misread your comment and confused mermaid_params with mermaid_cmd option.

Adding any additional parameters to mermaid_params does not work for my use case, because the -i / -o options are inserted first, such that they are passed to the wrong command (npx instead of mmdc in my case).

In fact, the -i / -o options should be added after the mermaid_params to prevent users from accidentally messing with these parameters. If that is changed, my change would be optional in the sense that I could also configure

mermaid_cmd = "npx"
mermaid_params = ["--no-install", "mmdc"]

However, the fact that this works is an implementation detail and feels wrong. The mermaid_cmd is actually npx --no-install mmdc, the arguments are no arguments to mermaid.

[slanzmich]

I pushed a few more commits. Let me know what you think and if I should squash any of them.

[mgaitan]

I guess the order may be important, so could you also update the readme to mention that mermaid_cmd could be a list?