Add proper unit tests to translate.js

[axic]

This should be in the form of providing fixtures, the JSON outputs from previous compiler versions, and comparing that against and expected translation.

At least the versions listed in https://github.com/ethereum/solc-js/blob/master/test/compiler.js#L643-L650 should be included.

[qwloh]

Hey I'm interested to work on this. Can I claim this issue?

[cameel]

Sure! Go ahead.

The link in the description is now outdated but looks like it was pointing at this list that's now in test/compiler.ts.

Also, just a heads up, we're currently in the process of transitioning to TypeScript, which is being done by @stephensli. Fortunately I see that his upcoming PR (#614) does not touch translate.ts at all and that file does not depend on other files from that PR so I think there should be no interference.

[qwloh]

Okay! Will try to submit a PR within the next few days.