Remove unnecessary whitespace, courtesy of Xcode.
Add better error reporting to “open” function. Add public function "printErrorAndExit".
Add function "open(forWriting:, overwrite:)" for writing and appending to files.

Also added func "temporaryDirectory" to XCTestCase_Additions.
Use the new "printErrorAndExit" function.
Move "temporaryDirectory" to new file Files.swift and rename it "tempdirectory".

Because it could be useful in scripts too.
Add script for testing reading and writing files.