Mailhog

- Add [mhsendmail](https://github.com/mailhog/mhsendmail) sendmail replacement
- Fix 42 - panic when setting UI bind address
- Fix 46 - utf8 error in e-mail subject
- Fix 41 and 50 - underscores replaced with spaces in UI
- Fix mailhog/MailHog-UI6 - user defined pagination
- Merge 43 and 44 - fix documentation, thanks eirc
- Merge 48 - fix documentation, thanks zhubert
- Merge mailhog/MailHog-Server1 - avoid duplicate headers, thanks wienczny

- Fix 24 - base64 attachments/mime part downloads
- Fix 28 - embed js/css/font assets for offline use
- Fix 29 - overview of MailHog for readme
- Fix 34 - message list scrolling
- Fix 35 - message list sorting
- Fix 36 - document outgoing SMTP server configuration and APIv2
- Merge mailhog/MailHog-UI4 - support base64 content transfer encoding, thanks stekershaw
- Merge mailhog/Mailhog-UI5 - single part encoded text/plain, thanks naoina

- Fix mailhog/MailHog-UI3 - squashed subject line

- Merge mailhog/data2 - MIME boundary fixes, thanks nvcnvn
- Merge mailhog/MailHog-UI2 - UI overhaul, thanks omegahm
- Fix 31 - updated this file :smile:

- Fix 22 - render non-multipart messages with HTML content type
- Fix 25 - make web UI resource paths relative

- Hopefully fix 22 - broken rendering of HTML email
- Partially implement 15 - authentication for SMTP release
- Load outgoing SMTP servers from file
- Save outgoing SMTP server when releasing message in UI
- Select outgoing SMTP server when release message in UI
- Make Jim (Chaos Monkey) available via APIv2
- Add Jim overview and on/off switch to web UI