Change compile to take in a JS object rather than a string.

The `compile` function takes in a string, when really it wants a well described JS object. In JS, this isn't much of a difference but when using something like TypeScript or Flow the difference is pretty significant as one gives you compile-time errors/warnings and auto-complete while the other (string input) gives you nothing useful.

An initial pass at the TS definitions can be found at https://github.com/MicahZoltu/solc-js/blob/ts-definitions/index.d.ts and discussion can be found at #205.

Start with the TypeScript definitions in index.d.ts and read the discussion in #205, then trace the compile API described in the issue. The change is complete when compile uses a well-described JavaScript object input and the TypeScript definitions provide useful type checking and autocomplete.

Written by the indexing model from the issue text.