How to: compress uploads
files can be autocompressed on upload,  either on user-request (if config allows) or forced by server-config

* volflag `gz` allows gz compression
* volflag `xz` allows lzma compression
* volflag `pk` **forces** compression on all files
* url parameter `pk` requests compression with server-default algorithm
* url parameter `gz` or `xz` requests compression with a specific algorithm
* url parameter `xz` requests xz compression

things to note,
* the `gz` and `xz` arguments take a single optional argument, the compression level (range 0 to 9)
* the `pk` volflag takes the optional argument `ALGORITHM,LEVEL` which will then be forced for all uploads, for example `gz,9` or `xz,0`
* default compression is gzip level 9
* all upload methods except up2k are supported
* the files will be indexed after compression, so dupe-detection and file-search will not work as expected

some examples,
* `-v inc:inc:w:c,pk=xz,0`  
  folder named inc, shared at inc, write-only for everyone, forces xz compression at level 0
* `-v inc:inc:w:c,pk`  
  same write-only inc, but forces gz compression (default) instead of xz
* `-v inc:inc:w:c,gz`  
  allows (but does not force) gz compression if client uploads to `/inc?pk` or `/inc?gz` or `/inc?gz=4`