Change root dir permission to 755.
Move functions to save/load id files to command/command.go
Move config.go from mackerel package to config package
Merge pull request #6 from mackerelio/root-dir-permission

Fix default root dir permission
Merge remote-tracking branch 'origin/master' into multi-platform

Conflicts:
	command/command.go
	metrics/linux/plugin.go
	metrics/linux/plugin_test.go