mjml 4.6.0 on Node.js Yarn

Features

Add preprocessors to mjml parser - Fixes #42, #874, #457, #459 (thanks @XBeg9)
Add "inner-background-color" to mj-column to improve gutter. You can set different background-colors for padding and content. Also adds "inner-border" and "inner-border-radius".
Add "letter-spacing" attribute to mj-button (thanks @milap1296)
Add "usemap" attribute to mj-image (thanks @vinikira)

Fix #1628 --filePath option accepts directories. Also, fix watch of nested includes when filePath is specified.
Fix #1670 mj-accordion fallback for Thunderbird (thanks @bertho-zero)
Fix #1801 dont escape url when "baseUrl" is set on mj-navbar
Fix mj-group background-color on outlook 2016 - set bgcolor on table (thanks @btd)
Fix invalid font-size value on p tag on mj-divider (thanks @allentsai93)
Fix #1848 cli --version alias
Allow "border-radius" to be percentage or px based on several components (thanks @zslabs)
Fix http links in code examples (thanks @edjw)
Multiple documentation improvements (thanks @GarryFlemings, @toantqt, @petetnt, @allanlewis, @davidsneighbour)