doc that popover content() is given the element as an arg; fix #13175
Fix HTML errors
Add Gist & Customizer URLs to customized files & config.json

Fixes #9951
Fixes #12865
grunt dist
Merge pull request #13205 from twbs/fix-9951

Add Gist & Customizer URLs to customized files & config.json
use glob instead of fs.readdirSync since /less now has subdirs
rename generateCustomCSS to generateCustomLess for accuracy
enhance customizer to handle transitive Less @import-s
grunt update-shrinkwrap build-customizer dist
Merge pull request #13047 from twbs/fix-customizer

Fix customizer (see #13043)
Merge pull request #13190 from twbs/fix-13175

doc that popover content() is given the element as an arg