/** \page usage Usage
 * 
 * This page provides general information on QuaZIP usage. See classes
 * QuaZip and QuaZipFile for the detailed documentation on what can
 * QuaZIP do and what can not. Also, reading comments in the zip.h and
 * unzip.h files (taken from the original ZIP/UNZIP package) is always a
 * good idea too. After all, QuaZIP is just a wrapper with a few
 * convenience extensions and reimplementations.
 *
 * QuaZip is a class representing ZIP archive, QuaZipFile represents a
 * file inside archive and subclasses QIODevice as well.
 *
 * \section terminology Terminology
 *
 * "QuaZIP" means whole this library, while "QuaZip" (not case
 * difference) is just one class in it.
 *
 * "ZIP/UNZIP API" means the original API of the Gilles Vollant's
 * ZIP/UNZIP package. I did not alter it in any way to make it easier to
 * port to the future ZIP/UNZIP versions.
 *
 * "ZIP", "ZIP archive" or "ZIP file" means any ZIP archive. Typically
 * this is a plain file with ".zip" (or ".ZIP") file name suffix.
 *
 * "A file inside archive", "a file inside ZIP" or something like that
 * means file either being read or written from/to some ZIP archive.
 *
 * \section error-handling Error handling
 *
 * Almost any call to ZIP/UNZIP API return some error code. Most of the
 * original API's error checking could be done in this wrapper as well,
 * but it would cause unnecessary code bloating without any benefit. So,
 * QuaZIP only checks for situations that ZIP/UNZIP API can not check
 * for. For example, ZIP/UNZIP API has no "ZIP open mode" concept
 * because read and write modes are completely separated. On the other
 * hand, to avoid creating classes like "QuaZipReader", "QuaZipWriter"
 * or something like that, QuaZIP introduces "ZIP open mode" concept
 * instead, thus making it possible to use one class (QuaZip) for both
 * reading and writing. But this leads to additional open mode checks
 * which are not done in ZIP/UNZIP package.
 *
 * Therefore, error checking is two-level (QuaZIP's level and ZIP/UNZIP
 * API level), which sometimes can be confusing, so here are some
 * advices on how the error checking should be properly done:
 *
 * - Both QuaZip and QuaZipFile have getZipError() function, which return
 *   error code of the last ZIP/UNZIP API call. Most function calls
 *   reset error code to UNZ_OK on success and set error code on
 *   failure. Some functions do not reset error code. Most of them are
 *   \c const and do not access ZIP archive in any way. Some, on the
 *   other hand, \em do access ZIP archive, but do not reset or set
 *   error code. For example, QuaZipFile::pos() function. Such functions
 *   are explicitly marked in the documentation.
 * - Most functions have its own way to report errors, by returning a
 *   null string, negative value or \c false. If such a function returns
 *   error value, call getZipError() to get more information about
 *   error. See "zip.h" and "unzip.h" of the ZIP/UNZIP package for error
 *   codes.
 * - If the function returns error-stating value (like \c false), but
 *   getZipError() returns UNZ_OK, it means that you did something
 *   obviously wrong. For example, tried to write in the archive open
 *   for reading or not open at all. You better just do not do that!
 *   Most functions also issue a warning using qWarning() function in
 *   such cases. See documentation for a specific function for details
 *   on when it should not be called.
 *
 * I know that this is somewhat messy, but I could not find a better way
 * to do all the error handling.
 **/