The gain, given the "real sites benchmark" below, is obvious:
```
benchmark old ns/op new ns/op delta
BenchmarkHugo-4 14497594101 13084156335 -9.75%
benchmark old allocs new allocs delta
BenchmarkHugo-4 57404335 48282002 -15.89%
benchmark old bytes new bytes delta
BenchmarkHugo-4 9933505624 9721984424 -2.13%
```
Fixes #2495
* Fall back to default language on missing translation file
* Add a i18n-warnings build flag
* If that flag is set, print a parseable and greppable string on missing translation strings
See #2303
This commit also consolidates URLs on Node vs Page, so now .Permalink should be interoperable.
Note that this implementations should be fairly short-livded, waiting for #2297, but the API should be stable.
Setting the language to use when loading the language bundles just doesn't work.
The template system is unfortanetely a global, and the last languate processed won ...
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..
