Add pagination support for home page, sections and taxonomies

Two new configuration properties, `Paginate` (default `0`) and `PaginatePath` (default `page`) are added.

Setting `paginate` to a positive value will split the list pages for the home page, sections and taxonomies into chunks of size of the `paginate` property.

A `.Paginator` is provided to help building a pager menu.

There are two ways to configure a `.Paginator`:

1. The simplest way is just to call `.Paginator.Pages` from a template. It will contain the pages for "that page" (`.Data.Pages` will (like today) contain all the pages).
2. Select a sub-set of the pages with the available template functions and pass the slice to `.Paginate` : `{{ range (.Paginate (where .Data.Pages "Type" "post")).Pages }}`

**NOTE:** For a given Node, it's one of the options above. It's perfectly legitimate to iterate over the same pager more than once, but it's static and cannot change.

The `.Paginator` contains enough information to build a full-blown paginator interface.

The pages are built on the form (note: BLANK means no value, i.e. home page):

```
[SECTION/TAXONOMY/BLANK]/index.html
[SECTION/TAXONOMY/BLANK]/page/1/index.html => redirect to  [SECTION/TAXONOMY/BLANK]/index.html
[SECTION/TAXONOMY/BLANK]/page/2/index.html
....
```

Fixes #96

1 files changed, 95 insertions, 0 deletions

diff --git a/hugolib/pagination_test.go b/hugolib/pagination_test.go
new file mode 100644
index 000000000..080866f6f
--- /dev/null
+++ b/hugolib/pagination_test.go
@@ -0,0 +1,95 @@
+package hugolib
+
+import (
+	"fmt"
+	"github.com/spf13/hugo/source"
+	"github.com/spf13/viper"
+	"github.com/stretchr/testify/assert"
+	"path/filepath"
+	"testing"
+)
+
+func TestSplitPages(t *testing.T) {
+
+	pages := createTestPages(21)
+	chunks := splitPages(pages, 5)
+	assert.Equal(t, 5, len(chunks))
+
+	for i := 0; i < 4; i++ {
+		assert.Equal(t, 5, len(chunks[i]))
+	}
+
+	lastChunk := chunks[4]
+	assert.Equal(t, 1, len(lastChunk))
+
+}
+
+func TestPaginator(t *testing.T) {
+
+	pages := createTestPages(21)
+	urlFactory := func(page int) string {
+		return fmt.Sprintf("page/%d/", page)
+	}
+
+	paginator := newPaginator(pages, 5, urlFactory)
+	paginatorPages := paginator.Pagers()
+
+	assert.Equal(t, 5, len(paginatorPages))
+	assert.Equal(t, 21, paginator.TotalNumberOfElements())
+	assert.Equal(t, 5, paginator.PageSize())
+	assert.Equal(t, 5, paginator.TotalPages())
+
+	first := paginatorPages[0]
+	assert.Equal(t, "page/1/", first.Url())
+	assert.Equal(t, first, first.First())
+	assert.Equal(t, true, first.HasNext())
+	assert.Equal(t, false, first.HasPrev())
+	assert.Equal(t, 5, first.NumberOfElements())
+	assert.Equal(t, 1, first.PageNumber())
+
+	third := paginatorPages[2]
+	assert.Equal(t, true, third.HasNext())
+	assert.Equal(t, true, third.HasPrev())
+
+	last := paginatorPages[4]
+	assert.Equal(t, "page/5/", last.Url())
+	assert.Equal(t, last, last.Last())
+	assert.Equal(t, false, last.HasNext())
+	assert.Equal(t, true, last.HasPrev())
+	assert.Equal(t, 1, last.NumberOfElements())
+	assert.Equal(t, 5, last.PageNumber())
+
+}
+
+func TestPaginationUrlFactory(t *testing.T) {
+	viper.Set("PaginatePath", "zoo")
+	unicode := newPaginationUrlFactory("новости проекта")
+	fooBar := newPaginationUrlFactory("foo", "bar")
+
+	assert.Equal(t, "/%D0%BD%D0%BE%D0%B2%D0%BE%D1%81%D1%82%D0%B8-%D0%BF%D1%80%D0%BE%D0%B5%D0%BA%D1%82%D0%B0/", unicode(1))
+	assert.Equal(t, "/foo/bar/", fooBar(1))
+	assert.Equal(t, "/%D0%BD%D0%BE%D0%B2%D0%BE%D1%81%D1%82%D0%B8-%D0%BF%D1%80%D0%BE%D0%B5%D0%BA%D1%82%D0%B0/zoo/4/", unicode(4))
+	assert.Equal(t, "/foo/bar/zoo/12345/", fooBar(12345))
+
+}
+
+func createTestPages(num int) Pages {
+	pages := make(Pages, num)
+
+	for i := 0; i < num; i++ {
+		pages[i] = &Page{
+			Node: Node{
+				UrlPath: UrlPath{
+					Section: "z",
+					Url:     fmt.Sprintf("http://base/x/y/p%d.html", num),
+				},
+				Site: &SiteInfo{
+					BaseUrl: "http://base/",
+				},
+			},
+			Source: Source{File: *source.NewFile(filepath.FromSlash(fmt.Sprintf("/x/y/p%d.md", num)))},
+		}
+	}
+
+	return pages
+}