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 also adjusts the pagination logic to allow for these new collections.
Note that we will follow up with a template function named `group` that will be the end user API. The `.Group` method on `Page` should be considered as internal.
Updates #4865
We still do lowering of the param strings in some internal use of this, but the exported `GetParam` method is changed to a more sensible default.
This was used for the `disqus_title` etc. in the internal Disqus template, which was obviously not right.
If you really want to lowercase your params, do it with `.GetParam "myparam" | lower` or similar.
Fixes#4187
This closes#98, even if this commit does not do full content text search.
We may revisit that problem in the future, but that deserves its own issue.
Fixes#98
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
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
`GroupBy` is modified to allow it to receive a method name argument for
example `Type` as its first argument. It is only allowed to call with
a method which takes no arguments and returns a result or a pair of
a result and an error.
The functions discussed at #443 are also added
- `ByPublishDate`: Order contents by `PublishDate` front matter variable
- `GroupByPublishDate(format, order)`: Group contents by `PublishDate`
front matter variable formatted in string like `GroupByDate`
- `GroupByParam(key, order)`: Group contents by `Param` front matter
variable specified by `key` argument
- `GroupByParamDate(key, format, order)`: Group contents by `Param`
front matter variable specified by `key` argument and formatted in
string like `GroupByDate`. It's effective against `time.Time` type
front matter variable
