correct documentation of some config elements

Closes #1380
Update metrics.rb example

Update the example because output doesn't have the message parameter, instead it should use a a codec.
Also update the way how logstash is executed.
Removed version info in LS command
Closes #1362
Add tilde to UNIXPATH

Tilde '~' is a valid character in UNIXPATHs.

Closes #1195
reject invalid UNIX timestamp
stronger regex and code-style change
fix failing test
use non-capturing group in float regex
Closes #1253
config grammar: Allow spaces in [field references][like this]

Tests included.

Note about grammar compilation:
  I had to use treetop 1.4.15 (1.5.3 generates ruby code that fails to
  parse, haven't spent any time debugging)

Fixes #1513
Adding delaycompress to logrotate

To avoid issues like:

/etc/cron.daily/logrotate:
gzip: stdin: file size changed while zipping

This change is harmless and will prevent errors like this one