Fix a bug that rabbit command always returns failure exit status
doc: fix layout
logger: require files explicitly

require_files_under_directory_in_load_path ignores exceptions while
loading. If window system can't be initialized, 'require "gtk2"' is
failed. But the exception is also ignored. Then rabbit command is
crashed on no window system environment such as "DISPLAY= rabbit".

[shocker-ja:1189]

Reported by Kazuhiro NISHIYAMA. Thanks!!!
Add missing require
Should install libsvg first.
Fix typo
Merge pull request #30 from lazywei/master

Add a dependency reminder in installation 

Patch by Bert Chang. Thanks!!!
doc: fix a typo

brew insatll ->
brew install
        ^^

It happens. :-)