Deprecations warnings disable API is broken

[rpominov]

After we switched to Rollup, we've accidentally broken the warnings disabling feature. It worked like this:

const kefir = require('kefir')
Kefir.DEPRECATION_WARNINGS = false

Not sure if this API can be preserved with Rollup, maybe we'll need to switch to something like the following in order to fix this:

const kefir = require('kefir')
Kefir.disableDeprecationWarnings()
Kefir.enableDeprecationWarnings()

[rvikmanis]

Hope this is not super critical, can do it probably next week.

[rpominov]

Thanks, @rvikmanis. That would be cool. Not critical at all as it seems to me.