Add support for history end_time param & make time parameter optional

[sibbl]

As documented in the REST API HA docs, there's another parameter end_time which is not covered by the API.

Furthermore, the timestamp field was made optional as this is also supported according to the HA docs.

I'd appreciate any feedback and am looking forward to getting this into the next version of this npm module. Thanks!

[DarkPark]

is this project dead?

[sibbl]

Probably ¯\_(ツ)_/¯

[DarkPark]

@sibbl that's a shame, it would be nice to be able to use NodeJS with HA

[mririgoyen]

Please make sure the unit tests continue to pass and new test cases are provided around your new functionality.