[Feature request] Add page handler

[StephanStanisic]

Something that I find lacking is the ability to add custom pages from plugins. Currently a plugin like the blog plugin and store plugin use a rather complex and convoluted way to create custom pages. My suggestion would be to incorporate into core, in order to make this usable.

Example usage of this:

<?php
global $Wcms;

// @param slug: string
// @param page_callback: callable
$Wcms->registerPage("blog", function($args){
    return [
        "title" => "My Blog",
        "description" => "Some description",
        "keywords" => "a, few, keywords",
        "content" => "Hello, world! " . json_encode($args)
    ];
});

Core could execute the function in argument 2 to get all information to construct a page. This would trigger as follows:

url /blog would call function with [] as argument
url /blog/foo would call function with ["foo"] as argument
url /blog/foo/bar/baz would call function with ["foo", "bar", "baz"] as argument

[robiso]

Hey @StephanStanisic, hope you're doing good.

With the latest version of WonderCMS, you can do this by using:
$Wcms->createPage('blog/foo', true);
$Wcms->updatePage('blog/foo', 'title', 'Lorem ipsum');

Example from the code in index.php where it's used:

	/**
	 * Update page data
	 *
	 * @param array $slugTree
	 * @param string $fieldname
	 * @param string $content
	 * @return void
	 * @throws Exception
	 */

$Wcms->updatePage($this->currentPageTree, $fieldname, $content);

In retrospect, this seems to achieve the same result:

$Wcms->registerPage("blog", function($args){
    return [
        "title" => "My Blog",
        "description" => "Some description",
        "keywords" => "a, few, keywords",
        "content" => "Hello, world! " . json_encode($args)
    ];
});
// Should be the same as.
$Wcms->createPage('blog', true);
$Wcms->updatePage('blog', 'title', 'My Blog');
$Wcms->updatePage('blog', 'description', 'Some description');
$Wcms->updatePage('blog', 'keywords', 'a, few, keywords');
$Wcms->updatePage('blog', 'content', "Hello, world! " . json_encode($args));

Please reopen the issue if this isn't approximately what you meant.