Add Carthage support

[pendolf]

When I try to install this package with Carthage, I've got an error:

*** Skipped building LightweightChartsIOS due to the error:
Dependency "LightweightChartsIOS" has no shared framework schemes

If you believe this to be an error, please file an issue with the maintainers at https://github.com/tradingview/LightweightChartsIOS/issues/new

More info: https://github.com/Carthage/Carthage#share-your-xcode-schemes