fix(waitforangular): improve error messages when waitForAngular fails

Previously, caught errors were being interpreted as an empty object, causing
lots of errors such as
'Uncaught exception: Error while waiting for Protractor to sync with the page: {}'
Now the error message will be displayed, and a more useful custom message
will be thrown if the variable 'angular' is not present or the root element
is not part of the ng-app.

See #1474
docs(locators): add info on interpolation markers for by.binding

See #1480
chore(docs): automatic doc generation, closes #1255
style(typo): fix typo introduced in d505249
docs(changelog): update changelog for v1.5.0 to note removal of getInstance

See #1614
chore(website): comments from 1606