Bug Fix: emacs html export

[aareman]

emacs html export requires the htmlize package which is no longer included in the latest orgmode for emacs (I'm using emacs 26.3). If you export to html -> emacs with a code block it breaks since it uses htmlize to syntax highlight. (btw, get the same error in emacs when trying to export)

That being said, when I install the htmlize package in emacs, exporting from emacs works, but still fails from orgmode.nvim. The reason is because the --batch flag doesn't source your emacs configuration and any packages you have. This PR adds a --load switch to the export command that points at your emacs config. This tells emacs running in batch mode to load a specific startup file, in this case the main emacs config.

NOTE Changes beyond this. We may want to have a config option for specifying the location of an emacs config to use, since its not standard on all systems.

I know its failing tests/formatting. Just want to make sure this is an acceptable fix before polishing this PR. (See NOTE above for one outstanding issue)

[kristijanhusak]

Didn't know about that, thanks. I guess this should also fix #87.
Only issue that I see with this is that it's hardcoded. People may be using different path like $HOME/.emacs for example.
Lets do this:

• Introduce a property emacs_config in the config/defaults.lua file that should look something like this:

emacs_config = {
  executable_path = 'emacs',
  config_path = '$HOME/.emacs.d/init.el`
}

• Use the above config in the exporter

That should solve everything, and make it configurable.

[aareman]

@kristijanhusak I've made the updates and fixed the formatting issues. I also added basic documentation for it in the DOC.md file, Is there anywhere else I should put it?

[kristijanhusak]

@aareman looks ok, just address that one comment, and please squash commits into a single one. Thanks.

[aareman]

I made the changes, and squashed the commits.

[kristijanhusak]

Awesome, thanks!