Add named params & outer origin to diff operation

[sculpt0r]

Add origin to the ckeditor4 repository which comes from CLI. Then diff target branch with a branch from that origin. Only if any slug for an external repository is passed and it can't be our ckeditor4 main repo slug.

So, the extra origin should be added only for PR's that come from other forks. This PR also requires changes in the travis.yml on the main repo. ~I'm going to prepare them.~ Please, take a look at: https://github.com/ckeditor/ckeditor4/pull/4972

Closes #19

[sculpt0r]

I added an argument parser, so we can use naming parameters. Since there is a lot of arguments - it will be easier to maintain them from the command line and inside the code. Since they are mostly dependent on the CI - it is hard to hold them inside the configuration json file.

[sculpt0r]

Ready for review:

• added .editorconfig since trimming the last empty line by VSC was a little bit frustrating
• added logs with exit codes - because the spawned process may exit properly, but with error code and data outputted on standard error output
• Bumped package version to 1.0.0 since we are introducing breaking change with naming parameters
• yargs parser was downgraded to be compatible with Node 10

https://github.com/ckeditor/ckeditor4/pull/4972 PR contains changes that should be synced with this PR. The Travis cfg temporarily uses this repo on this branch (until we create the first release). Also, there is a dummy change in one plugin to verify if diff query is generating properly. This change should be reverted before the actual merge.