Add Zip support

Resolves com-lihaoyi#161. Add Zip
support.

`os.zip(path)` to read/write zip file. File will be created if not
exists.

`zipFile / subPath` to get a path. Should be able to support all the
file operations like copy, move, delete and so on.

os/src/ZipOps.scala

@@ -0,0 +1,22 @@
+package os
+
+import java.net.URI
+import java.nio.file.{Path => _, _}
+import collection.JavaConverters._
+
+
+class zip(zipPath: Path) {
+
+  private val fs = FileSystems.newFileSystem(
+    URI.create("jar:file:" + zipPath.wrapped.toString),
+    Map("create" -> "true").asJava)
+
+  def path(path: Path): Path = new Path(fs.getPath(path.wrapped.toString))
+  def root(): Path = path(os.root)
+  def /(sub: PathChunk): Path = root() / sub
+  def close(): Unit = fs.close()
+}
+
+object zip extends Function1[Path, zip] {
+  def apply(path: Path): zip = new zip(path)
+}

os/test/src/ZipTests.scala

@@ -0,0 +1,39 @@
+package test.os
+
+import test.os.TestUtil.prep
+import utest._
+
+import scala.collection.immutable.Seq
+
+object ZipTests extends TestSuite {
+
+  // on unix it is 81 bytes, win adds 3 bytes (3 \r characters)
+  private val multilineSizes = Set[Long](81, 84)
+
+  def tests = Tests {
+
+    test("zipOps") {
+
+      test - prep { wd =>
+        val zipFile = os.zip(wd / "zip-test.zip")
+        os.copy(wd / "File.txt", zipFile / "File.txt")
+        os.copy(wd / "folder1", zipFile / "folder1")
+        os.copy(wd / "folder2", zipFile / "folder2")
+        zipFile.close()
+
+        val zipFile2 = os.zip(wd / "zip-test.zip")
+        os.list(zipFile2.root()).map(_.toString) ==>
+          Vector(os.root / "File.txt", os.root / "folder1", os.root / "folder2").map(_.toString)
+        os.remove.all(zipFile2 / "folder2")
+        os.remove(zipFile2 / "File.txt")
+        zipFile2.close()
+
+        val zipFile3 = os.zip(wd / "zip-test.zip")
+        os.list(zipFile3.root()).map(_.toString) ==> Vector(os.root / "folder1").map(_.toString)
+        zipFile3.close()
+
+      }
+    }
+  }
+
+}