Add support for partial updates

[amitayh]

The REST API allows partial updates to documents:
https://www.elastic.co/guide/en/elasticsearch/guide/current/partial-updates.html

It is, however, not supported in Flummi (as far as I could see). This would be very helpful.

Thanks!

[micharegel]

Hi amitayh,

would you like to write some tests and code to support partial updates? Please fork flummi and send us a pull request.

Kind regards,
micha

[amitayh]

Thanks for the reply,
I'll try :)

BTW, when are you going to release the next version? I saw you already added support for source filters, but it's not available in v0.21.0 yet

[micharegel]

I just released 0.22.0 with the latest changes

[amitayh]

Great, thanks!