Misc readme updates
Use context rather than arg in README examples
Update block helper docs in README

Fixes #231, #259
Merge branch 'master' of github.com:wycats/handlebars.js
Fix for issue #517.

Now when compiiled with amd option and a single input argument, we are
checking to see whether the input is a file or folder.
Merge pull request #533 from blessenm/amd-precompilation-fix

Fix for the issue #517
Fix typo
Update testing notes

Fixes #467
Use better variable name
Merge branch 'master' of github.com:wycats/handlebars.js