added 'files' param to 'save' smooth function
refactored BasicReadAndWriteSmoothTest into FileSmoothTest
added FileSetSmoothTest
added NewFileFunction
refactored FileSmoothTest
renamed File.createInputStream() -> openInputStream()
renamed MutableFile.createOutputStream() -> openOutputStream()
renamed FileSystem.createInputStream() -> FileSystem.openInputStream(), FileSystem.createOutputStream() -> FileSystem.openOutputStream()