Modularity for SFX archives

[schnaader]

When using Precomp for self extracting archives, the following would be useful to reduce their size:

• Remove code not used for SFX (e.g. on-the-fly compressions, verbose mode, ...)
• Remove or adjust code like command-line parsing, syntax help
• Remove all decompression code, only use recompression code
• Removing all unused recompression methods (e.g. if only PNG and JPG were used, remove all others)

This could be done using modular concepts, e.g. using #ifdefs or treating recompression methods as plug-ins.