docs(guide): add ng-book link to books

Closes #4792
docs(guide): add ng-newsletter to weekly updates link

Closes #4793
docs($http): improve $http's caching documentation

Make the possibility to pass a custom cache instance to $http more obvious.

Closes #4803
docs(ngdoc): clarify extra module installation options

Closes #4811
docs(guide/understanding_controller): fix incorrect property reference

Correct " model property `spice` " to " model property `customSpice` " to match the code sample

Closes #4812
docs(guide): fix typo

Closes #4821
docs(errors/compile/tplrt): display html block as code

HTML elements were getting parsed by as HTML elements

Closes #4827
docs($httpBackendSpec): fix typo in spy name

Closes #4830