Adding Keyword classes for handling of TAL keywords.

Classes were added for 'default' and 'nothing', as well as an
interface, which extends Countable.  Countable is used
to determine thruthiness by other methods
Adding tests for Keyword classes, JSON update

Keyword interface implements JsonSerializable for compatibility
with the json: modifier.

Tests of the keyword classes added
Merge pull request #16 from ajcrites/keyword_classes

Keyword classes
Skip hard to fix failing test

I know, I know…
PHP 5.3 compatibility
Removed compatibility with PHPTAL 1.1 code generator
Skip locale tests when system has no Fr locale
Method name changed to testUmlaut #17
Merge pull request #18 from pornel/umlaut

Method name changed to testUmlaut #17
Allow backslashes in tales modifiers, so we can use namespaced classes.
Closures: Creating initial test for #20
Updating Closure evaulation handling.
Adding Closure support for boolean, repeat, and omit-tag
Fixing syntax for omit-tag boolean check

instanceof apparently requires an argument that can be an object instance,
but this is not always the case
Closures: updating test for PHP 5.2 compatibility
Closures: updating test for proper use with tal:replace
Closures: adding test to confirm non-closure analogs also work
Closures: Updating check for closure call for data type compatibility
Closures: adding tests for contained and nested closures
Supporting nested closures