Migrate to ES6

[valmynd]

Hello,

I did a port to ES6, maybe you're interested in taking over the changes.
I'm sorry that I did a lot of reformatting, that makes up a bulk of the changes in the diffs...

The tests are running fine, I don't know if I should've added the dist-folder to the .gitignore-file?

Anyway, thanks for your awesome implementation of CIEDE2000!

[coveralls]

Coverage increased (+0.7%) to 100.0% when pulling cb809b8 on valmynd:master into ad7d2da on markusn:master.

[coveralls]

Coverage increased (+0.7%) to 100.0% when pulling ebf22f1 on valmynd:master into ad7d2da on markusn:master.

[markusn]

Hi! Thanks for the PR, I will have a look at it when I get the time (this week is a bit busy). As you already stated the dist folder should not be part of the git-repo (it should be in the .gitignore file) as it is a build artifact (this should be fixed before the PR is accepted).

[coveralls]

Coverage increased (+0.7%) to 100.0% when pulling 2b7b52e on valmynd:master into ad7d2da on markusn:master.

[markusn]

I've tried to have a look at the diff, however it is very hard due to the fact that most of the changes is reformatting, shadowing the actual changes related to ES6. The reformatting should be removed, it makes it hard to review and does (in my opinion) not add any benefits.

The structure of the files also changed: the structure used in the source files should be divided into sections in the following order: imports/exports, followed by the definitions of exported functions, followed by internal functions. This structure is there for a good reason: when examining a source file it should be immediately obvious which imports and exports it has and after that the interesting (public) functions should be defined (followed by the uninteresting internal functions).