Add tests with numeric literals
Treat numbers as numbers in expressions

This is so that `{{ 1 }} ` is treated as `1` and not as `model.1`.
Same goes for `{{ 1.2 }}` which should not be treated as `model.1.2`.

Fixes #24
Merge pull request #26 from arv/numeric-litarals-in-expressions

Numeric litarals in expressions