preamble_size: Consolidate table formatting, align columns better

Before
./preamble_size.py
SSH command size: 759
Bootstrap (mitogen.core) size: 18227 (17.80KiB)

                              Original          Minimized           Compressed
mitogen.parent            98853 96.5KiB  51103 49.9KiB 51.7%  12881 12.6KiB 13.0%
mitogen.fork               8445  8.2KiB   4139  4.0KiB 49.0%   1652  1.6KiB 19.6%
mitogen.ssh               10827 10.6KiB   6893  6.7KiB 63.7%   2099  2.0KiB 19.4%
mitogen.sudo              12089 11.8KiB   5924  5.8KiB 49.0%   2249  2.2KiB 18.6%
mitogen.select            12325 12.0KiB   2929  2.9KiB 23.8%    964  0.9KiB 7.8%
mitogen.service           41581 40.6KiB  22398 21.9KiB 53.9%   5847  5.7KiB 14.1%
mitogen.fakessh           15767 15.4KiB   8149  8.0KiB 51.7%   2676  2.6KiB 17.0%
mitogen.master            55317 54.0KiB  28846 28.2KiB 52.1%   7528  7.4KiB 13.6%

After:
SSH command size: 759
Bootstrap (mitogen.core) size: 18227 (17.80KiB)

                        Original           Minimized           Compressed
mitogen.parent        98853  96.5KiB  51103 49.9KiB 51.7%  12881 12.6KiB 13.0%
mitogen.fork           8445   8.2KiB   4139  4.0KiB 49.0%   1652  1.6KiB 19.6%
mitogen.ssh           10827  10.6KiB   6893  6.7KiB 63.7%   2099  2.0KiB 19.4%
mitogen.sudo          12089  11.8KiB   5924  5.8KiB 49.0%   2249  2.2KiB 18.6%
mitogen.select        12325  12.0KiB   2929  2.9KiB 23.8%    964  0.9KiB  7.8%
mitogen.service       41581  40.6KiB  22398 21.9KiB 53.9%   5847  5.7KiB 14.1%
mitogen.fakessh       15767  15.4KiB   8149  8.0KiB 51.7%   2676  2.6KiB 17.0%
mitogen.master        55317  54.0KiB  28846 28.2KiB 52.1%   7528  7.4KiB 13.6%

preamble_size.py

@@ -18,6 +18,16 @@ import mitogen.service
 import mitogen.ssh
 import mitogen.sudo
 
+
+class Table(object):
+    HEADERS = (' ', 'Original', 'Minimized', 'Compressed')
+    HEAD_FMT = '{:20} {:^15}  {:^19}  {:^19}'
+    ROW_FMT =  '%-20s %6i %5.1fKiB  %5i %4.1fKiB %4.1f%%  %5i %4.1fKiB %4.1f%%'
+
+    def header(self):
+        return self.HEAD_FMT.format(*self.HEADERS)
+
+
 router = mitogen.master.Router()
 context = mitogen.parent.Context(router, 0)
 options = mitogen.ssh.Options(max_message_size=0, hostname='foo')
@@ -36,16 +46,8 @@ if '--dump' in sys.argv:
     exit()
 
 
-print(
-    '                           '
-    ' '
-    '  Original   '
-    '  '
-    '     Minimized     '
-    '  '
-    '    Compressed     '
-)
-
+table = Table()
+print(table.header())
 for mod in (
         mitogen.parent,
         mitogen.fork,
@@ -63,13 +65,7 @@ for mod in (
     compressed = zlib.compress(minimized.encode(), 9)
     compressed_size = len(compressed)
     print(
-        '%-25s'
-        ' '
-        '%5i %4.1fKiB'
-        '  '
-        '%5i %4.1fKiB %.1f%%'
-        '  '
-        '%5i %4.1fKiB %.1f%%'
+        table.ROW_FMT
     % (
         mod.__name__,
         original_size,