* Convert `js/util.js` to Typescript and add tests
Besides converting `js/util.js` to Typescript, this change also adds
`js/types.ts` that defines common types used in apple2js. Some of
these types, like `byte` and `word` are for information only.
* Convert `js/base64.js` to Typescript
This also adds a new type, `memory`, that is either an array of
numbers, or a Uint8Array.
* Convert `js/ram.js` to Typescript
This change does not convert `RAM` to a class; it just introduces types.
* Basic typing of cpu6502
This is a really rough first pass. There are some problems that can't
be fixed until this is turned into a real class, but at least all of
the function arguments are now typed. This caught a few cases where
extra arguments were being passed in.
* Convert `js/cpu6502` to a class
In theory, idiomatic classes should be better than the previous
closure-based classes. However, this conversion shows that the
instruction table does not fit well with idiomatic classes as method
referenced in the table need to be called with the correct `this`
everywhere.
This should, at best, be considered a first attempt.
