This extends the page grouping in Hugo with a template function that allows for ad-hoc grouping.
A made-up example:
```
{{ $cool := where .Site.RegularPages "Params.cool" true | group "cool" }}
{{ $blue := where .Site.RegularPages "Params.blue" true | group "blue" }}
{{ $paginator := .Paginate (slice $cool $blue) }}
```
Closes#4865
This commit expands the Resource interface with 3 new methods:
* Name
* Title
* Params
All of these can be set in the Page front matter. `Name` will get its default value from the base filename, and is the value used in the ByPrefix and GetByPrefix lookup methods.
Fixes#4244
Note that this looks like overkill for just the logger, and that is correct,
but this will make sense once we start with the template handling etc.
Updates #2701
Page.GroupByParam function internally uses Page.GetParam to get a
parameter value for a key of a page group but now Page.GetParam returns
a lowercase character string every time. It has no need to using
lowercase character string as a group key value and it confuse a
function user.
This fixes it to keep and return an original parameter string as a group
key value.
Fix#1564
File handling was broken on Windows. This commit contains a revision of the path handling with separation of file paths and urls where needed.
There may be remaining issues and there may be better ways to do this, but it is easier to start that refactoring job with a set of passing tests.
Fixes#687Fixes#660
Following issues are fixed
1. Can't access fields and methods specified in GroupBy call
2. PagesGroup doesn't contain Pages. It's always empty.
3. When GroupBy is called with Section key, it doesn't work as expected
