Enable to configure archive columns (all besides the file name)

[Doron Behar]

In #61, I discussed a bit the idea of configurable archive columns. Here's a more accurate proposal:

Make it possible to specify archive files output format, where the file name always appears at the end. The filename should always appear at the end, since their length could be too long for us to predict in advance. We don't want to make pistol read beforehand the file names and decide on the padding such that it will print nicely.

The columns to be printed will be decided by parsing an environment variable with comma-separated values, in which order matters, and is reflected in the output.

Perhaps an additional environment variable, or using a more sophisticated parsing of the above env var, will specify what columns should have lower and higher priority. The low priority columns will not get printed if the output terminal window has too low number of columns.