detects only drops longer than 1s

Previously it was possible to only use size - 1B, because filling the
whole buffer would make start and end indices equal, making the buffer
appear empty. This is important if we want to allow direct zero-copy
access to the buffer while storing multi-byte elements.

Allow tile_limit = 0 as indicated by the help.

+ small fixes in that struct

It was introduced by mistake with the commit 09426b2a.

- print which parameter has incorrect value (bitrate, mem_limit, tile_limit)
- check also quality and pool size

- allow also comma as a delimiter (WLOG - comma cannot be part of
  current set of options)
- print token, that is not understood
- hint that "bps" must be in bits-per-second (% 8 = 0)

Fixed a situation when audio compression changes BPS, eg. AAC:

    uv -s testcard --audio-codec AAC --audio-capture-format channels=2

If using libcineform with pkg-config, set proper CINEFORM_LIB and do not
override CINEFORM_INC.