moved TestingFileSystem to org.smoothbuild.testing package
fixed caught exception in InMemoryFileSystem
added TestingFileSystem.assertContentHasFilePath()
Added validation of path arguments to all InMemoryFileSystem methods
added SaveToFunction
added Path.projectRootPath(),currentDirPath()
removed Function.result(), result is simply returned by Function.execute()
added TestingFileContent, TestingFileRw, TestingFilesRw
refactored tests to use new testing classes