Refactor packages

[andrewl33]

Description

This is purely a refactor. There are no logic changes.

The comments and changelogs are probably not up-to-date any longer. 😬

There was a problem with circular dependencies at some point during the creation of this repo.
I believe this solves that problem, by layering the codebase like this:

The pattern for users will be to use mostly types, api and client.

Other improvements?

I don't know the codebase well enough to understand how reasonable these recommendations are.

• rename types and client to aptostypes and aptosclient. They'll probably clash codebases that import this sdk.
• Put client-only types in the client library. Merge api and client.
• Make a constants package? For 0x1... etc.
• Based on usage, users will probably care about 3 distinct things, Account management, transaction creation, and interacting with the node. Maybe that should guide further package shuffles.

Test Plan

The multiple main_test.go still build. I added ./scripts/build-tests.sh to verify.