Add multilingual support in Hugo

Implements:
* support to render:
  * content/post/whatever.en.md to /en/2015/12/22/whatever/index.html
  * content/post/whatever.fr.md to /fr/2015/12/22/whatever/index.html
* gets enabled when `Multilingual:` is specified in config.
* support having language switchers in templates, that know
  where the translated page is (with .Page.Translations)
  (when you're on /en/about/, you can have a "Francais" link pointing to
   /fr/a-propos/)
  * all translations are in the `.Page.Translations` map, including the current one.
* easily tweak themes to support Multilingual mode
* renders in a single swift, no need for two config files.

Adds a couple of variables useful for multilingual sites

Adds documentation (content/multilingual.md)

Added language prefixing for all URL generation/permalinking see in the
code base.

Implements i18n. Leverages the great github.com/nicksnyder/go-i18n lib.. thanks Nick.
* Adds "i18n" and "T" template functions..

1 files changed, 41 insertions, 0 deletions

diff --git a/commands/multilingual.go b/commands/multilingual.go
new file mode 100644
index 000000000..68da7c96d
--- /dev/null
+++ b/commands/multilingual.go
@@ -0,0 +1,41 @@
+package commands
+
+import (
+	"sort"
+
+	"github.com/spf13/cast"
+	"github.com/spf13/viper"
+)
+
+var langConfigs map[string]interface{}
+var langConfigsList langConfigsSortable
+
+func readMultilingualConfiguration() {
+	multilingual := viper.GetStringMap("Multilingual")
+	if len(multilingual) == 0 {
+		langConfigsList = append(langConfigsList, "")
+		return
+	}
+
+	langConfigs = make(map[string]interface{})
+	for lang, config := range multilingual {
+		langConfigs[lang] = config
+		langConfigsList = append(langConfigsList, lang)
+	}
+	sort.Sort(langConfigsList)
+}
+
+type langConfigsSortable []string
+
+func (p langConfigsSortable) Len() int           { return len(p) }
+func (p langConfigsSortable) Less(i, j int) bool { return weightForLang(p[i]) < weightForLang(p[j]) }
+func (p langConfigsSortable) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+
+func weightForLang(lang string) int {
+	conf := langConfigs[lang]
+	if conf == nil {
+		return 0
+	}
+	m := cast.ToStringMap(conf)
+	return cast.ToInt(m["weight"])
+}