Fix spelling issues
Improve exception handling

- Rename ignored exception parameters to "ignored" so as to make it
  explicit that ignoring the exception is intentional
- Remove exception types not thrown from throws clauses
- Throw IOException if File.mkdir|mkdirs returns false. Until now the
  result was just ignored.
Remove unused Downloader constructor
Call main methods of other classes with empty String[] instead of null
Use "%n" instead of "\n" in calls to PrintStream.printf
Rename JsoupFilter.hasIndexLink to missingIndexLink to avoid negation
Several minor refactorings, e.g. simplified boolean expression
Update MD5s for it_handbuch, shell_prog

TODO: Check if cleaner still works as expected after archive has changed
Upgrade Java/AspectJ source/target levels to 1.7

Now that Java 7 has been released on all relevant platforms (even MacOS)
a while ago, this should not be problematic anymore.

TODO: Get rid of Apache Commons Compress, use fixed JDK ZIP classes.
Upgrade AspectJ 1.7.1 to 1.7.4
Add IntelliJ IDEA project, but ignore a few files/directories
Reorganise some imports
Use Java 7 diamond syntax for generics constructors
FindBugs: explicitly set encoding when writing files
Cosmetics: spelling, whitespace, superfluous CLI parameters
Enhancement: handle truncated (partly downloaded) ZIP file gracefully

Throw exception with message: "Probably the download of <zipFile> was
interrupted. Please delete the file and retry."
Bugfix: handle illegal book ID correctly
Switch file encoding of JsoupFilter.java to UTF-8

Converted from ISO-8859-1. This affects special characters in regexes
  - TITLE_PREFIX_POSTFIX
  - TITLE_DASHED_BOOK_PREFIX
  - TITLE_CHAPTER
Bugfix: ankerNode in createIndexLink() was not cloned

Furthermore, the case that no ankerNode to be cloned is found in DOM is
now handled by throwing a RuntimeException with message: "Cannot create
index link because no cloneable TOC node has been found (should never
happen)"
BasicTracingAspect: make static member 'stream' private