better formatting of accrued costs

[durka]

Uses printf, fixed-width fields, and bc for a better-formatted table (why aren't we charged for use of printf and bc?). Not tested very heavily. Formatting will break when the total or individual count reaches 10^7.

Sample:

=======================
Welcome to GNU Pricing!
=======================

Using many GNU tools now cost $0.01 per use.

This command (gcc) has been used 6 times so far.

Overall GNU command usage
 command   usage   cost
--------- ------- ------
 basename      21 $0.21
      cat      48 $0.48
       cp       9 $0.09
  dirname       1 $0.01
     echo       7 $0.07
      gcc       6 $0.06
     grep     144 $1.44
       ln       7 $0.07
       ls      14 $0.14
    mkdir      27 $0.27
       mv      67 $0.67
      pwd       2 $0.02
       rm      78 $0.78
      sed      25 $0.25
    uname      28 $0.28
     uniq       3 $0.03
--------- ------- ------
    Total     487 $4.87

Please pay the total cost at https://donate.fsf.org/