Don't evaluate lambdas that return falsy values as an empty string.

Issue: If I create a Mustache lambda to return numbers and I expect 0 to be of
those numbers, I'll instead only receive an empty string for 0 because it
evaluates to falsy.

Fix: Check the result of the lambda to be undefined or null. Only then should
it return the empty string.
performance fix for ipads & iphones
Merge pull request #273 from woledzki/master

Performance fix for iphones and ipads
Merge pull request #264 from mattsacks/check-falsy

Don't evaluate lambdas that return falsy values as an empty string.
Fail gracefully on empty template

Fixes #267
Merge remote-tracking branch 'upstream/master'
Version 0.7.1
Use mocha for testing
Add compiled templates overview and examples to readme
Merge pull request #280 from buymeasoda/docs-for-compile

Add compiled templates overview and examples to readme
Style tweaks
clean up and standardize UMD wrapper
handle case where exports is null
Merge pull request #283 from busticated/amdwrapper

clean up and standardize UMD wrapper
Better error reporting
Add failing test for nested higher-order sections
Fixed rendering error when using nested higher-order sections

Fixes #274
Merge remote-tracking branch 'upstream/master'
Update CHANGES
Version 0.7.2