Use shorter alias for package names

[cubismic]

Some package names are too long. (e.g. primitives)
It hurts code readability while importing and using the package that has a long name.

Use alias for long package name like prims for primitives

[cubismic]

@majecty Do you think this is necessary?
I think this doesn't have a high priority for now.
Currently, 17 files refer primitives package 8 times on average.

[majecty]

I don't think that we must fix this issue before the alpha release.