Multi-literal strings support

[k06a]

Description

We need support for multi-literal strings like this:

bytes32 constant public HUMAN_TYPEHASH = keccak256(
    "Human("
    "string name,"
    "string surname,"
    "string street,"
    "address wallet,"
    "uint256 age,"
    "uint256 birth"
    ")"
);

Here is demo repo: https://github.com/k06a/truffle-string-multi-literal

Check Solidity Grammar:

Steps to reproduce

1. git clone "https://github.com/k06a/truffle-string-multi-literal"
2. cd truffle-string-multi-literal
3. npm install or yarn
4. npm lint or yarn lint

Expected behavior

This is valid Solidity code.

Operating System

macOS 10.11.2

Linter version

Solium version 1.2.5