fix support for elasticsearch v7 + add types

[robyte-ctrl]

opened the PR in here by mistake (meant to merge it in my fork's master branch) so feel free to close it

but this PR does fix #166 and it also adds types so it's easier to use this library in a typescript project

[mcollina]

Good work!

This is a semver-major change, right?

[robyte-ctrl]

Good work!

This is a semver-major change, right?

@mcollina shouldn't be, although I have renamed some of the options so that they follow the camelCase naming notation, the old names still work and I've added some tests to make sure that they do

if you want to remove the old names completely then that would be a semver-major change

[mcollina]

I see you have removed --bulk-size from the CLI options, hence my guess.

[robyte-ctrl]

I see you have removed --bulk-size from the CLI options, hence my guess.

@mcollina oh, right, I removed it because it wasn't doing anything

not sure how that could be considered deprecated since a deprecation usually means that the deprecated thing still works

have I perhaps missed something?

should I add it back and leave it as is just to keep the interface the same?

[mcollina]

ah no worries! That's ok.