Convert.js/Base58.js Cleanup

Changes all the function signatures in `convert.js` and `base58.js` to use the regular function notation and explicitly adds module exports at the end of the file (as per convention).

As indicated in #56, indentation has also been adjusted to 2 space soft-tabs.

This should be reviewed commit by commit, as the changes are most clear in isolation.
And on the surface, a lot of code has been touched.