Ignore empty strings on list iteration.

From: https://github.com/christianchristensen/mustache.go/commit/060a7128c162b14d125bf4abcec7706624899dae
Add more informative error message when partial is not found.

From: https://github.com/hiteshjasani/mustache/commit/43048009fb39b3fd44c3f84c888346b0bdbdd0ee
Combine redundant parsing code.

From: https://github.com/choongng/mustache/commit/a0df8266e2f4b0a0ace21bfdc5e4b76c6df89462