Replace `var` with `auto`

[axic]

This is not a mature proposal yet, but the benefit is that it discourages the use of var, since auto needs some prior reading from the user.

[chriseth]

... you mean a user that assumes Solidity == Javascript?

[axic]

For a C++ user it will be clear types are derived automatically and a Javascript user wouldn't be inclined to use var as they could be today.

[axic]

... you mean a user that assumes Solidity == Javascript?

That is the assumption by many and was even suggested by old documentation.

[axic]

var has been deprecated in #3301. Closing this now.