Add imageConfig function which calls image.DecodeConfig and returns the height, width and color mode of the image. (#2677)
This allows for more advanced image shortcodes and templates such as those required by AMP.
layouts/shortcodes/amp-img.html
```
{{ $src := .Get "src" }}
{{ $config := imageConfig (printf "/static/%s" $src) }}
<amp-img src="{{$src}}"
height="{{$config.Height}}"
width="{{$config.Width}}"
layout="responsive">
</amp-img>
```
This commit adds a `GitInfo` object to `Page` if `EnableGitInfo` is set.
It then also sets `Lastmod` for the given `Page` to the author date provided by Git.
The Git integrations should be fairly performant, but it adds "some time" to the build, somewhat depending on the Git history size.
If you want, you can run without during development and turn it on when deploying to the live server: `hugo --enableGitInfo`.
Fixes#2102
- removed comma on line 16 to avoid confusion between clauses
- added period to line 24 for consistency
- clarified "read on" on line 30 to follow style above it while
also verbally writing what the author seems to intend
- removed "You probably know what to do." on line 30 due to wordiness
that could lead to confusion and a drag in reading speed
- changed preposition into intended infinitive for syntactical clarity
- removed "easily" as it doesn't describe anything technical and is
confusing (which is why the author may have used a preposition)
All config variables starts with low-case and uses camelCase.
If there is abbreviation at the beginning of the name, the whole
abbreviation will be written in low-case.
If there is abbreviation at the end of the name, the
whole abbreviation will be written in upper-case.
For example, rssURI.
This change adds a canonical alias.html template that is used for page
redirects, and passes the page as data to the template under .Page
Fixes#2533Closes#2576
