The markdown renderer passes its output through an HTML pretty printer.
While this is good in most cases, it makes a mess of elements that expect
their content to be left untouched.
The pretty printer already ignores `pre` tags (and other built-ins) by
default. This fix allows us to specify other tags that should be left
alone.
Further it actually specifies this option for `code-example` and `code-pane`
tags, which expect to contain preformatted content.
All the docs related files (docs-app, doc-gen, content, etc)
are now to be found inside the `/aio` folder.
The related gulp tasks have been moved from the top level
gulp file to a new one inside the `/aio` folder.
The structure of the `/aio` folder now looks like:
```
/aio/
build/ # gulp tasks
content/ #MARKDOWN FILES for devguides, cheatsheet, etc
devguides/
cheatsheets/
transforms/ #dgeni packages, templates, etc
src/
app/
assets/
content/ #HTML + JSON build artifacts produced by dgeni from /aio/content.
#This dir is .gitignored-ed
e2e/ #protractor tests for the doc viewer app
node_modules/ #dependencies for both the doc viewer builds and the dgeni stuff
#This dir is .gitignored-ed
gulpfile.js #Tasks for generating docs and building & deploying the doc viewer
```
Closes#14361
Pete Bacon Darwin