Fix typeo: we would be then be able -> we would then be able

Closes #13
Fix typeo: demonstate -> demonstrate

Closes #15
Fix typeo: a method of allowing content respond to its container’s dimensions -> a method of allowing content to respond to its container’s dimensions

Closes #16
Fix typeo: to facilitate the constuction of layouts -> to facilitate the construction of layouts

Closes #17
Merge pull request #18 from peterwilsoncc/gh-pages

Fix typos