Add offline support

[rnevius]

Description

Adds layouts, styles, and build processes for generating offline documentation (e.g. PDFs). For now, PDFs should be generated manually via Adobe Acrobat.

Resolves #1647

Motivation and Context

Customers would like to access Sensu docs offline and on e-reader devices.

Review Instructions

1. Run a local hugo server with offline layouts

   yarn run server --layoutDir=offline
   

2. Navigate to http://localhost:1313/ and select your product/version of choice. Note the URL of this resource.

3. Open Acrobat and File → Create → PDF from Web Page

   

[rnevius]

@cwjohnston here's an example of a generated PDF: Sensu Go 5.13 - Sensu Docs.pdf

An issue that should be apparent right away is that SVG images aren't rendered by Acrobat. We could replace these with PNGs as needed.

[hillaryfraley]

Hi @rnevius ! I'm working on trying this out -- I seem to have some trouble at the yarn run server --layoutDir=offline point. Here's what happens in terminal:

---

Never mind, I needed to switch to your branch! facepalm

[rnevius]

@hillaryfraley have you switched to this branch? The "postcss:develop" grunt task should be processing 2 stylesheets and generating 2 sourcemaps...so it almost seems like some of the source files are missing.

[hillaryfraley]

Yes, that was it, thank you -- sorry I didn't realize it sooner.
Just PDFd 5.0!

[rnevius]

It also appears that Acrobat doesn't render/capture emoji (such as the ✅ which is used in supported platform tables).