* remove the $enable-flex variable option
* remove bootstrap-flex.css dist file and it's grunt task
* remove the separate flex css file for docs; it's all the same now
* remove flexbox docs (porting some to the main grid docs in next commit)
* clean up few grid docs bits to simplify copy, start to mention flexbox
* port relevant flexbox-grid.md content to grid.md
- clean up mixins
- update how it works section
- bring over sizing and alignment sections
* remove the $enable-flex from the options.md page
* update lead paragraph to mention flexbox
* update migration to mention loss of ie9 support
* remove mention of flexbox dist file
* clarify IE support
* making a note
* remove flexbox variant mentions from component docs
- updates docs for media object, navs, list group, and cards to consolidate docs
- no more need to callout flexbox variants since it's now the default
* remove $enable-flex if/else from sass files
* remove flex dist files
* update scss lint property order to account for flex properties
* linting
* change to numberless classes for autosizing, wrap in highlighting div
* bump gruntfile and postcss to ie10
* redo intro sections
* rearrange
* phew, redo hella grid docs
- rearrange all the things
- consolidate some bits
* remove reference to flexbox mode
* more border action for demo
* Make some changes to the .card's in .card-deck's to ensure footers align to the bottom
* Explore responsive display utils, but with a twist: lowest breakpoint has no breakpoint modifier in the class name
* make floats use the same format, add float-none mixin
* descriptions for getting started pages
* descriptions for layout
* add content page descriptions
* more descriptions, updates to some existing ones
* correct site url
* add social stuff to config for twitter cards
* add twitter meta tags; use large image for homepage and regular card for all others
* add the assets
* more site config
* more social shiz to partial, remove existing meta for the partial, remove page title from homepage for simpler if statements
* Add .img-fluid to card images in columns to ensure proper resizing
* change that variable from regular value to variable
* use calc to figure out a tighter border for card images
"Go somewhere" is more descriptive of an example link, rather than a
button that triggers in-page functionality. Also makes it consistent
with all other examples in this page
These can be replaced by their `.text-xs-*` parallels.
This also avoids any complications from interactions between the responsive and non-responsive classes.
(e.g. `<div class="text-left text-md-right">`)
Refs #18300
[skip sauce]
