Merge branch 'refs/heads/t/compress'

A short series which overhauls the algorithm behind the compress
filter and its documentation.

Cooking for almost a year.

* refs/heads/t/compress:
  compress: Overhaul the meaning of --aggressiveness.
  compress: Apply damping later.
  compress: Warn when samples are clipped.
  compress: Document and sanity-check command line options.
  compress: Fix off by one in help of --target-level.

diff --cc NEWS.md
index d8813b3f3e484a27bf06593826162923d020e996,55ef3be947ee76d6b0937b33988b0cd960c0e985..50ec0a3a51e156b704cf6979ec595f83a300192e
--- 1/NEWS.md
--- 2/NEWS.md
+++ b/NEWS.md
@@@ -1,19 -1,6 +1,21 @@@
  NEWS
  ====
  
- 
 +----------------------------------------------
 +0.6.3 (to be announced) "generalized activity"
 +----------------------------------------------
 +
 +- The ff command now accepts a negative argument to instruct the
 +  virtual streaming system to jump backwards in the current audio
 +  stream. The old syntax (e.g., "ff 30-") is still supported but it
 +  is deprecated and no longer documented. The compatibility code is
 +  sheduled for removal after 0.7.0.
 +- para_afh: New option: --preserve to reset the modification time to
 +  the value of the original file after meta data modification.
++- Overhaul of the compress filter code. The refined algorithm should
++  reduce clipping. The meaning of --aggressiveness has changed, see the
++  updated and extended documentation of the compress filter for details.
 +
  --------------------------------------
  0.6.2 (2018-06-30) "elastic diversity"
  --------------------------------------