New filter unit tests

- pluralize
- script_tag
- stylesheet_tag
- upcase
Fixed stylesheet_tag filter

Added a slash to close the link tag.
Fixed upcase filter

Removed condition which checked if the input was a stringValue.
Merge branch 'new-tests'
Merge pull request #49 from joeldrapper/new-tests

New filter unit tests
Merge pull request #50 from joeldrapper/upcase

Fixed stylesheet_tag filter
Merge pull request #51 from joeldrapper/stylesheet

Fixed upcase filter
Merge branch 'master' of https://github.com/9miles/gaze