Swift4 multiline support

[kenji21]

Tailor Version: v0.1.0
master

Swift Version: 1.0
4.0

Platform (Mac/Linux/Windows/CI): Mac
Mac

Installation Method: Homebrew

Steps to Reproduce Issue

1. Add some multiline string vars to StringAndCharacters.swift test file:

let multilineString = """
multiline
text
"""

let multilineStringWithVar = """
multiline
text
with a star \(star)
"""

let multilineStringWithEscaped = """
  You could write multi-lined strings
  without "escaping" single quotes.
"""

Expected Behavior

No test failure

Actual Behavior

java.lang.AssertionError:
Expected: an empty string
but: was "line 8:24 extraneous input '"' expecting {, ';', 'for', 'case', ......

when running GrammarTest::testGrammar