Enable "--includes" option at reading configuration.

For configurations in another config file by include.path.
(I put github.token and github.oauth-token in another config file.)

For information about "--includes" option, see the following URL.
http://git-scm.com/docs/git-config#_includes
#3

create a new option `yagist-git-config-with-includes'

enforce error handle while calling git command.
colorize readme
version up