feat: correct implementation of partial block

[sunng87]

Fixes #698 #696

This patch finally reimplements partial's block context correctly. The key is to remove all previous blocks and use a separated one for partial.

It corrects behavior of partial parameter, hash and merge_json:

• if parameters is provided, either as path or literal, use it as base value; otherwise use this as base_value
• if hash is provided, always merge it with base value:
  • if base value is associative type: object, array, string, merge them as map
  • if base value is non-associative type, return hash
    otherwise, use base value directly

When partial is rendered, reset blocks.

Tests added.

[coveralls]

coverage: 82.233% (+0.3%) from 81.928%
when pulling cf2a8d0 on fix/partial-context-merge
into e9c4fe7 on master.

[hrydgard]

Thank you!

[sunng87]

Just trying to validate on your project.

[sunng87]

@hrydgard it should work now. I will look into another partial issue tomorrow and cut a release soon.