Implement @root property

Handlebars added an @root property to look up the root context in
https://github.com/wycats/handlebars.js/commit/cb80f4684323f2924d4251eeb3d7b12cc37ea6d
This adds equivilent support in lightncandy in a non-invasive manner.
Implement extended comment syntax {{!-- --}}

This syntax is available in handlebars.js, could be hidden behind a feature
flag if desired.
Implement {{else}} in each and section context
Merge pull request #29 from ebernhardson/each-else

Implement {{else}} in each and section context
Merge pull request #27 from ebernhardson/extended-comments

Implement extended comment syntax {{!-- --}}
Merge pull request #26 from ebernhardson/access-root-context

Implement @root property
Auto generated tests from Travis [ci skip]
update history. support {{@root.foo.bar}}
Auto generated tests from Travis [ci skip]
fix unittest
nothing
update history
tab -> 4 spaces
update doc
new extended helper encode/escape logic, fix php warning
Merge pull request #31 from zordius/helper_escape_logic

new extended helper encode/escape logic, fix php warning
fix typo in doc. update history
version up
remove unused var in gen_test.php
Auto generated tests from Travis [ci skip]