Convert page_url to an AsTag

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Switched to version from https://github.com/okfn/foundation, also added a test.

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Update documentation for page_url accordingly.

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
More accurate documentation

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Return empty string on lookup failures when used as AsTag, also, test this.

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Return '' when var_name is supplied, but set the value to None as appropriate.

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Updated test

In this test, we use template logic to emit 'DNE' if the page is not found and the AsTag returned None.

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Implementation refactored for render_tag as per @ojii

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Remove render_tag() block, return ''

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Remove commented out code (oops)

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Further refine docs

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Merge pull request #2760 from mkoistinen/page_url_as_tag

Convert page_url to an AsTag (RTM)