* Change it's to its.

* Fix links

* Fix typos

fixes #21423 by updating docs to mention flex display instead of inline-block; clarifies follow-up text about use of the proper utilities

* #20936 make inline checkbox/radio markup same as stacked

* tweak language and remove extra blank line in snippet

* fix form-inline with flex enabled
* grunt
* fix alignment of labels
* shorter if syntax
* add new form example to docs for now
* update inline form docs usage guidelines
* responsive margins
* better margin utils
* fix sizing of .form-check
* flexbox alignment of .form-check
* no need to change direction
* support custom controls in inline form, for default and flex modes
* add example of custom select and checks to docs
* remove hidden and visible label variants since we cover that in the usage guidelines at the start and include hidden labels everywhere
* use property value instead of layout name
* apply to all labels
* add a visible label, space it out
* add id

- Remove margin-bottom override in favor of .mb-0 utility class
- Apply the input line-height styles to match
- Remove the min-height to match the input

* 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

- Update docs examples to use newer .form-check suite of classes
- Update form validation mixin to use newer classes as well

Remember, there may be children/students using these examples...

- Includes new class
- New docs to support it
- Rearranged older docs

- Add lighter gray text to disabled state for .form-check
- Separate radios and checkboxes example
- Clarify docs

- Move disabled radio and checkbox styles to Reboot
- Collapse .radio and .checkbox into single class, .form-check
- Collapse .radio-inline and .checkbox-inline into single class, .form-check-inline
- Require classes for sub-elements in both new classes

Fixes #18573: Change name of .form-control-label to .col-form-label (and .form-control-legend to .col-form-legend) to reiterate use for only grid layouts

- Give some guidance on when someone might use any of the three
validation states. Fixes #18702.

- Improve the examples to provide examples of supporting validation
text with the new `.form-control-feedback`, as well as always-present
help text. Nullifies #18704.

Uses a new more specific class, adds some basic spacing, and clarifies
that this class is only for validation feedback.

Clears up the help text class question in
https://github.com/twbs/bootstrap/pull/18704#issuecomment-168241731 and
addresses the vertical spacing in #18703.

- Add container to fix padding in mobile views
- Add large and small variations
- Cross link grid classes and mixins
- Fix up some words