allow to override the default behaviour for showtoc

[merikan]

.. with sitewide param in config.toml

since showtoc is by default true you how to add 'showtoc: false' to all your blog posts if you dont want the toc beeing added.

keep the same behaviour as before but with the addition that you can now add a showtoc as a sitewide param in config.toml to change the default behaviour (fallback value).

Site Variable	Page Variable	show toc?
null	null	yes
null	false	no
null	true	yes
false	null	no
false	false	no
false	true	yes
true	null	true
true	false	no
true	true	yes

[zhaohuabing]

Hi @merikan it's nice, thanks.