Experimental conversion to Objective-C

We can now upgrade to a less restrictive license as well, since we
are no longer using libpipeline.
Check _currentOutputDirCreated, not _currentOutputDir

Fixes copying files when the output dir hasn't been created yet.
Style fixes
Added FLAC, Vorbis plugins
Option not to transcode specified extensions
Print a message explaining dry-run mode

Otherwise users might think the changes were actually made.
Use normalized paths so we can compare them
Prevent overwriting the input file
Use paths instead of URLs everywhere

Makes the code cleaner, we really just need the paths.
Implement deleting extraneous files
Move the stack logic to the directory visitor

This will enable us to implement renaming filters in an elegant way.
The renamed path components will be added to the stack.
Implemented renaming filters
Get rid of the SCVPlugin protocol

Merge those methods into the SCVPlugin class. That division was
meant to make a more clear distinction between the methods that
the plugins had to override and the helper methods that they could
leverage. In practice, this led to excessive casting.
Updated the manual page
Updated INSTALL, ChangeLog
A better README