update box-sizing third party support section to include mention of google CSE and expand to include CSS and Less options. mo betta docs on box-sizing to build on e521ee8

BS3 commits e521ee83094f5a70978cc9d879f400c3ac95369c,
36afdbcaac504117d515240cc7294c3fcbde4e45
Disabling responsiveness' section of docs: simplification and focus

BS3 commit a4897aed8889c614778bbfd92db60f5592ecde07
Refactoring the paragraph describing the 'Examples' section.

BS3 commit b0803471065d394cff280f9af1a0642f5e1c03b9
fixes 10372: two download buttons on homepage; also fixes broke button styles. shorten bootstrap config variables

BS3 commit 49373b9b45facc07e6a99223021536c9878dd2b2
fix download section. more consistency with Bootstrap. remove the callout, a zip should now be provided