Add option to define fade-out time for filenames and other text

[GoogleCodeExporter]

What steps will reproduce the problem?
1. get a huge log with a lot of commits
2.  --file-idle-time 0 --seconds-per-day 0.1 --auto-skip-seconds 1 
--max-file-lag 0.1 --hide filename


What is the expected output? 
I would expect the animation to be faster in all aspects: also the time after 
which the filename/dirname vanishes should depend on the duration of a single 
day. 

What do you see instead?
A lot of text cramped in a single place.
Look at 
http://www.youtube.com/watch?feature=player_detailpage&v=p2ixMJAJzlU#t=39s


What version of the product are you using? On what operating system?
Gource v0.40
Windows XP

Please provide any additional information below.

This software is the coolest!

Original issue reported on code.google.com by [email protected] on 27 May 2013 at 1:41