custom configuration file option

[abgit]

If we have multiple access logs with different formats we cannot use just one config.
With a new commandline option we could define a new "goaccessrc" config file.

eg:

goaccess -p /home/me/goaccessrc1 -f access_format1.log
goaccess -p /home/me/goaccessrc2 -f access_format2.log

this diff is related to feature request 9.

best,

[allinurl]

Thanks for the contribution. Feel free to pull the changes.