added building smooth-all.jar instead of smooth.jar, added building smooth.zip release file
improved error message in CommandLineError
refactored DiskFileSystem
added DiskFileSystem constructor taking projectRoot
added TestCaseWithTempDir
redesigned FileSystem.isDirectory() -> pathExistsAndIsDirectory()
refactored RecursiveFilesIterable
fixed TestingStream
added TestingJdkFile
added tests for DiskFileSystem