Define repo structure

[andrew-fleming]

We should define the structure for how the repo should be organized. There will be many more features coming from contracts, testing, tooling, and midnight, so this should be treated as a working "standard" until things start to mature

[andrew-fleming]

Define witnesses in witnesses/ directory #11 (comment)

[andrew-fleming]

Use PascalCase for compact contract names/modules #1 (comment)

[andrew-fleming]

Proposed structure:

contracts
    └──token
          └──src
              ├──ERC20.compact
              ├──ERC721.compact
              ├──test/
              └──witnesses/

test
  ├──mocks
       ├──MockERC20.compact
       └──MockERC721.compact
  ├──simulators
       ├──index.ts
       └──(...).ts
  ├──types
       ├──index.ts
       └──(...).ts
  └──utils
       ├──index.ts
       └──(...).ts
  ├──ERC20.test.ts
  └──ERC721.test.ts

witnesses
    ├──index.ts
    └──(...).ts