Updates sinon-chai definition and tests to support loading sinon-chai as a chai plugin.

- usage is as follows:
    import sinonChai = require('sinon-chai');
    chai.use(sinonChai);
- Also updates the tests to compile with --noImplicitAny

Technically this is two separate changes: updating the definitions to support `chai.use()` and fixing the tests to play nice with --noImplicitAny.  Let me know if I need to split this into two commits.