fix: correct partial-block render

[sunng87]

Fixes #697
Fixes #711

This patch updates how we render @partial-block. When rendering a partial include directive, the partial-block is now rendered before the partial, and when the inner partial tries to referencing @partial-block, we use the rendered content directly.

[coveralls]

coverage: 83.707% (+0.03%) from 83.673%
when pulling abe1b6c on fix/nested-partial-block-scope
into c349c39 on master.