The main motivation of this commit is to add a `page.Page` interface to replace the very file-oriented `hugolib.Page` struct.
This is all a preparation step for issue #5074, "pages from other data sources".
But this also fixes a set of annoying limitations, especially related to custom output formats, and shortcodes.
Most notable changes:
* The inner content of shortcodes using the `{{%` as the outer-most delimiter will now be sent to the content renderer, e.g. Blackfriday.
This means that any markdown will partake in the global ToC and footnote context etc.
* The Custom Output formats are now "fully virtualized". This removes many of the current limitations.
* The taxonomy list type now has a reference to the `Page` object.
This improves the taxonomy template `.Title` situation and make common template constructs much simpler.
See #5074Fixes#5763Fixes#5758Fixes#5090Fixes#5204Fixes#4695Fixes#5607Fixes#5707Fixes#5719Fixes#3113Fixes#5706Fixes#5767Fixes#5723Fixes#5769Fixes#5770Fixes#5771Fixes#5759Fixes#5776Fixes#5777Fixes#5778
Thanks to @bep's new, brilliant helpers.Deprecated() function,
the following functions or variables are transitioned to their
new names, preserving backward compatibility for v0.14
and warning the user of upcoming obsolescence in v0.15:
* .Url → .URL (for node, menu and paginator)
* .Site.BaseUrl → .Site.BaseURL
* .Site.Indexes → .Site.Taxonomies
* .Site.Recent → .Site.Pages
* getJson → getJSON
* getCsv → getCSV
* safeHtml → safeHTML
* safeCss → safeCSS
* safeUrl → safeURL
Also fix related initialisms in strings and comments.
Continued effort in fixing #959.
Prior to this commit, `HasMenuCurrent` and `IsMenuCurrent` on `Node` always returned false.
This made it hard (if possible at all) to mark the currently selected menu item/group for non-Page content (home page, category pages etc.), i.e. for menus defined in the site configuration.
This commit provides an implementation of these two methods.
Notable design choices:
* These menu items have a loose coupling to the the resources they navigate to; the `Url` is the best common identificator. To facilitate a consistent matching, and to get it in line with the menu items connected to `Page`, relative Urls (Urls starting with '/') for menu items in the site configuration are converted to permaLinks using the same rules used for others’.
* `IsMenuCurrent` only looks at the children of the current node; this is in line with the implementation on `Page`.
* Due to this loose coupling, `IsMenuCurrent` have to search downards in the tree to make sure that the node is inside the current menu. This could have been made simpler if it could answer `yes` to any match of any menu item matching the current resource.
This commit also adds a set of unit tests for the menu system.
Fixes#367
