docs(downloading): fix invalid filenames and add missing modules

Closes #4846
docs(misc/contribute): fix internal links

Closes #4848
docs(tutorial/step-12): fix incorrect code filename

Closes #4860
docs(resource): fix grammatical issue

'Case' should be the plural 'cases' since it is talking about multiple possible cases rather
than a single case. For slightly more info, see the section 'When words like "none" are the
subject' in this article: http://writing.wisc.edu/Handbook/SubjectVerb.html
docs(guide/directive): clarify sentence meaning

Closes #4873
docs(guide/directive): split long lines
docs(tutorial/step-2): remove repeated "the"

Closes #4854
docs($q): add missing closing parentheses in code example

Closes #4900
docs(guide/concepts): improve sentence wording

Before:

> Let's add some more logic to the example to
allow to enter and calculate the costs in different currencies and also pay the invoice.

After:

> Let's add some more logic to the example that
allows us to enter and calculate the costs in different currencies and also pay the invoice.

Closes #4903
docs(NgModelController): clarify documentation of `$setViewValue`

$setViewValue does not really "Read a value from view".
It should be called to trigger the ngModel to be updated when the value in the view changes.

Closes #4907
Merge branch 'master' of https://github.com/angular/angular.js
componentizd!