Added string.htmlEncode and string.htmlDecode.
Template changes:
1. Only valid operator now is '='. Only valid math operator is modulo
'%'. '=' only will work with string and number. For boolean oprator isn't required.
2. 'not' operator added.
3. Ability to add custom tags.
4. Optional '#' prefix to if,for,custom tag. Might become mandatory someday.
5. Data refs are html encoded now.
Updated docs and examples.