clarify docs regarding non-mixable components
Fixes #12210: badges in xs buttons
Merge branch 'master' of github.com:twbs/bootstrap

Conflicts:
	docs/assets/js/customize.min.js
Merge pull request #12231 from twbs/callouts

callout severity tweaks
Merge pull request #12232 from twbs/mixing-docs

clarify docs regarding non-mixable components
Merge branch 'master' into docs_derp

Conflicts:
	docs/components.html
	docs/css.html
Set Jekyll encoding and tweak Windows notes
indentation and page header changes
Merge pull request #12241 from twbs/jekyll-encoding

Set Jekyll encoding and tweak Windows notes
add a couple commas
Getting Started: fix ID of heading so matches TOC
Fix page headers
Merge branch 'master' of github.com:twbs/bootstrap
remove inaccurate comment
add link to Sass CONTRIBUTING file in the About page
Remove popovers from components.html lead

because they're only really featured on javascript.html
Replacement: input groups
Adhere to MailChimp's brand guidelines ;)
Merge pull request #12242 from twbs/sass-contributing

add link to Sass CONTRIBUTING file in the About page
move Community & Translations docs sections from About to Getting Started
Merge pull request #12243 from twbs/cleanup-about

move Community & Translations docs sections from About to Getting Started