feat(config): use yml.load to support custom js types

[JLHwung]

The safeLoad method is recommended for untrusted data. However, hexo uses js-yaml to parse config files handwritten by SAs. These config files should be treated as trusted data and thus we can use load method for flexibility. The load method uses DEFAULT_FULL_SCHEMA to support !!js/regexp or !!js/function types.

This commit does not introduce breaking change as DEFAULT_FULL_SCHEMA is a superset of DEFAULT_SAFE_SCHEMA, which is defaults of safeLoad.

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[coveralls]

Coverage remained the same at 97.219% when pulling 3d88929 on load-all-types-on-js-yaml into bccee83 on master.

[NoahDragon]

Just not confident about this change. I saw many issues related to the wrong format of config file. What happened if the yaml file is corrupt? The load will continue parsing the correct parts?

[JLHwung]

@NoahDragon I don't think the corruption behavior of safeLoad differs to the one of load.

As from the documentation and the code, the only difference between safeLoad and load is the schema support: The load has support of !!js/regexp, !!js/undefined and !!js/function type schema other than safeLoad. The safeLoad calls load under the hood but pass in restricted schema.

We can add corruption behavior test on js-yaml though.

[NoahDragon]

Thank you. Then I think it is good for us.

[NoahDragon]

LGTM