hooks: shareable settings with defaults

[davidsneighbour]

We have hooks that execute and print code in our templates. How about having some form of pluggable truth giving variables.

Sample:

in the config:

[truther]
some.parameter.name = false

in the layout:

{{ with (site.Params.some.parameter.name | default true) }}
do something
{{ end }}

Sure, this could be on a per template/theme base, but with a reusable system this could be used to enable/disable date display, comment forms on a global or even local (frontmatter params) level and reuse documentation for these settings.

The executing code could be some form of

{{ if partial "truths.html" (dict 
                 "variable" "some.parameter.name" 
                 "value" "local value" 
                 "default" true) }}
do something
{{ end }}

and the partial could take care of sanitisation, comments in the CLI output, collection of available settings, etc.