highlight error message using hiecho

Add new method hiecho, which will highlight output message.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Commit log subject must start with "l10n:"

New verify method: verify_commit_log_subject, which will check whether
subject has proper prefix ("l10n:").

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>