Use object-assign instead of lodash.assign for smaller build

[danielkcz]

Closes #95 Partially solves #86

Actually don't merge yet, I've found this, could be another interesting option: https://github.com/rollup/rollup-plugin-inject

[koresar]

The work done here was migrated to stampit module. This compose implementation does not need to be tiny or performant because it serves as an example only.

Cheers!