Append values to the existing namespace instead of override.

[nesskyy]

Hi! In some situations, to keep consistency, there is a need to use the same window namespace for custom solutions as we might use for assigning data via @javascript(). Current implementation of the module overrides data that have been declared before @javascript(). What do you think about appending data to the namespace if such already exists (and maybe even make it configurable?) instead of just clearing that?

[freekmurze]

I'd like to keep this package very simple. Currently it supports only our usecases. If you need extra funtionality, feel freek to fork our code.