support/scripts: add size-stats-compare script

support/scripts: add size-stats-compare script

Leverage the CSV files produces by size-stats (make graph-size) to allow
for a comparison of rootfs size between two different buildroot
compilations.

The script takes the file-size CSV files of two compilations as input, and
produces a textual report of the differences per package.
Using the -d/--detail flag, the report will show the file size changes
instead of package size changes.
The -t/--threshold option allows to ignore file size differences smaller
or equal than the given threshold (in bytes).

Example output is:

Size difference per package (bytes), threshold = 0
--------------------------------------------------------------------------------
       -8192         busybox
      228572   added dmalloc
      301584   added jq
--------------------------------------------------------------------------------
      521964         TOTAL

or with detailed view:

Size difference per file (bytes), threshold = 0
--------------------------------------------------------------------------------
       -8192         bin/busybox
       18152   added usr/bin/jq
       39252   added usr/bin/dmalloc
       46968   added usr/lib/libdmalloc.so
       47288   added usr/lib/libdmallocxx.so
       47316   added usr/lib/libdmallocth.so
       47748   added usr/lib/libdmallocthcxx.so
      283432   added usr/lib/libjq.so.1.0.4
--------------------------------------------------------------------------------
      521964         TOTAL

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>