Remove TemporaryDirectory

This violates the responsibility of this framework.

Tests/PathTests/TemporaryDirectory.swift

@@ -0,0 +1,54 @@
+@testable import Path
+import Foundation
+
+class TemporaryDirectory {
+    let url: URL
+    var path: Path { return Path(string: url.path) }
+
+    /**
+     Creates a new temporary directory.
+
+     The directory is recursively deleted when this object deallocates.
+
+     If you need a temporary directory on a specific volume use the `appropriateFor`
+     parameter.
+
+     - Important: If you are moving a file, ensure to use the `appropriateFor`
+     parameter, since it is volume aware and moving the file across volumes will take
+     exponentially longer!
+     - Important: The `appropriateFor` parameter does not work on Linux.
+     - Parameter appropriateFor: The temporary directory will be located on this
+     volume.
+    */
+    init(appropriateFor: URL? = nil) throws {
+      #if !os(Linux)
+        let appropriate: URL
+        if let appropriateFor = appropriateFor {
+            appropriate = appropriateFor
+        } else if #available(OSX 10.12, iOS 10, tvOS 10, watchOS 3, *) {
+            appropriate = FileManager.default.temporaryDirectory
+        } else {
+            appropriate = URL(fileURLWithPath: NSTemporaryDirectory())
+        }
+        url = try FileManager.default.url(for: .itemReplacementDirectory, in: .userDomainMask, appropriateFor: appropriate, create: true)
+      #else
+        let envs = ProcessInfo.processInfo.environment
+        let env = envs["TMPDIR"] ?? envs["TEMP"] ?? envs["TMP"] ?? "/tmp"
+        let dir = Path.root/env/"swift-sh.XXXXXX"
+        var template = [UInt8](dir.string.utf8).map({ Int8($0) }) + [Int8(0)]
+        guard mkdtemp(&template) != nil else { throw CocoaError.error(.featureUnsupported) }
+        url = URL(fileURLWithPath: String(cString: template))
+      #endif
+    }
+
+    deinit {
+        _ = try? FileManager.default.removeItem(at: url)
+    }
+}
+
+extension Path {
+    static func mktemp<T>(body: (Path) throws -> T) throws -> T {
+        let tmp = try TemporaryDirectory()
+        return try body(tmp.path)
+    }
+}