Update to handle Dropbox's OAuth2.
Fixed `keep_mtime` option bug in HTTP location.
Merge branch 'dropbox' into webclient-special
Add concept of message log receiver, this is the abstraction of output
and format for message logs.
Add `--parent-front` option to `pione-client`.
Fixed `--parent-front` option of `pione-client` as no requisite.
Fixed `pione-client` command to connect the parent front.
Change @thread of `Command::Spawner` to be public.
Fix handling problem of broken links about `Util::Zip.compress`.
Merge remote-tracking branch 'origin/zip-bugfix' into webclient-special
Use kramdown command instead of redcarpet.
Merge remote-tracking branch 'origin/use-kramdown' into webclient-special
Fix stability of front server and child command connections.
Merge remote-tracking branch 'origin/more-stable-front' into webclient-special

Conflicts:
	lib/pione/command/basic-command.rb
Show more freindly error message.
Add `pione config` subcommand.
Merge remote-tracking branch 'origin/more-stable-front' into pione-config
Make sure mtime is different.
Make ignore spawn errors when the command is terminating.
Merge branch 'more-stable-front' into pione-config