mail support
add default sender capability, tune the APIs little bit
make the template rendering works
can render both the html & txt template, if exists
adjust the APIs a little bit
use Buffer as internal body, some api changes too
should encoding the mail subject correctly
add MailSender interface, with this, I can easily implment SendGrid mailer instead of smtp
add mock unit tests
#379: return 500 on not-exist public file path
typo...
Merge remote-tracking branch 'origin/master' into issue_379
a simpler patch
Merge pull request #292 'arkxu/master' into develop
Define an APP_VERSION variable when building

The contents of the variable are determined from the environment
variable of the same name, or from the output of "git describe" if the
environment variable is unset, and if the source is in a git repository.
The variable is defined in the "<ImportPath>/app" module.
Merge pull request #413 from abustany/develop

Define an APP_VERSION variable when building
Importing module routes under the parent path