Removed UTF-8 forced encoding in variable varule escaping, and replaced htmlentities with htmlspecialchars.

- Multiline bracket notation is no longer allowed for expressions because of
  JavaScript/CSS clashes.
- Variables in expressions can now be preceded by characters unequal to `$',
  which will be prefixed to the variable evaluation.

- The Template class represents a template file, consisting of blocks and
  variables.
- The Node class is used to create a tree structure of the blocks in a
  template file, and of the data that is mapped on the blocks.