scope styles to masthead, not homepage
Merge branch 'master' of github.com:twbs/bootstrap
don't be repetitive on homepage
expo callout copy
remove confusing comment
remove default left-right print margins per upstream h5bp change

Refs:
    https://github.com/h5bp/html5-boilerplate/commit/57be193031b95b003b96efe9eba7a4db7f58f4e1
    https://github.com/h5bp/html5-boilerplate/issues/1477
add docs note to address #12078
Merge pull request #12345 from twbs/printer-wackiness-note

add note about printer viewport weirdness
Fixes #12344: Update docs to show workaround for using button element with justified button groups
Merge branch 'master' of github.com:twbs/bootstrap
Merge pull request #12250 from twbs/rm-print-margins

remove default left-right print margins per upstream h5bp change
Merge branch 'master' of github.com:twbs/bootstrap
Fix #11655: Fix broken disabled states for iOS form controls and buttons
Follow-up to #12250: remove remaining page margins for print