Remove backticks from author names passed to gnuplot.

Without this, author names containing `touch /tmp/vulnerable` would cause said
file to appear after generating statistics for the given repository.

This is not an optimal solution. Instead of blacklisting characters we should
either whitelist some, or find a safe escape mechanism for gnuplot.
Bump README python requirement to 2.6.0.

The code already checks for python 2.6.
fix: let "Pool" for line count data collection honor "processes" configuration setting

Signed-off-by: Heikki Hokkanen <hoxu@users.sf.net>