minidump_dump: add proper cli processing
minidump_dump: add proper cli processing

In preparation for adding more flexibility to this tool, add a
proper parser for the command line flags.  This uses the style
as seen in other breakpad tools.

BUG=chromium:598947

Change-Id: I95495e6ca7093be34d0d426f98a6c22880ff24a3
Reviewed-on: https://chromium-review.googlesource.com/457019
Reviewed-by: Mark Mentovai <f1b5a91d4d6ad523f2610114591c007e75d15084@chromium.org>

bittorrent/breakpad,bittorrent/breakpad,bittorrent/breakpad,bittorrent/breakpad,bittorrent/breakpad,bittorrent/breakpad,bittorrent/breakpad