We have been using `go-toml` for language files only. This commit makes it the only TOML library.
It's spec compliant and very fast.
A benchark building a site with 200 pages with TOML front matter:
```bash
name old time/op new time/op delta
SiteNew/Regular_TOML_front_matter-16 48.5ms ± 1% 47.1ms ± 1% -2.85% (p=0.029 n=4+4)
name old alloc/op new alloc/op delta
SiteNew/Regular_TOML_front_matter-16 16.9MB ± 0% 16.7MB ± 0% -1.56% (p=0.029 n=4+4)
name old allocs/op new allocs/op delta
SiteNew/Regular_TOML_front_matter-16 302k ± 0% 296k ± 0% -2.20% (p=0.029 n=4+4)
```
Note that the front matter unmarshaling is only a small part of building a site, so the above is very good.
Fixes#8801
This commit started out investigating a `concurrent map read write` issue, ending by replacing the map with a struct.
This is easier to reason about, and it's more effective:
```
name old time/op new time/op delta
SiteNew/Regular_Deep_content_tree-16 71.5ms ± 3% 69.4ms ± 5% ~ (p=0.200 n=4+4)
name old alloc/op new alloc/op delta
SiteNew/Regular_Deep_content_tree-16 29.7MB ± 0% 27.9MB ± 0% -5.82% (p=0.029 n=4+4)
name old allocs/op new allocs/op delta
SiteNew/Regular_Deep_content_tree-16 313k ± 0% 303k ± 0% -3.35% (p=0.029 n=4+4)
```
See #8749
Hugo 0.76.0 updated go-i18n from v1 to v2. This allowed us to set the TOML unmarshaler to use, so we set the one we use in other places in Hugo.
But that does not support dotted bare keys, which caused some breakage in the wild.
This commit fixes that by:
* Using go-toml for language files
* Updating go-toml to the latest version
This commit implements Hugo Modules.
This is a broad subject, but some keywords include:
* A new `module` configuration section where you can import almost anything. You can configure both your own file mounts nd the file mounts of the modules you import. This is the new recommended way of configuring what you earlier put in `configDir`, `staticDir` etc. And it also allows you to mount folders in non-Hugo-projects, e.g. the `SCSS` folder in the Bootstrap GitHub project.
* A module consists of a set of mounts to the standard 7 component types in Hugo: `static`, `content`, `layouts`, `data`, `assets`, `i18n`, and `archetypes`. Yes, Theme Components can now include content, which should be very useful, especially in bigger multilingual projects.
* Modules not in your local file cache will be downloaded automatically and even "hot replaced" while the server is running.
* Hugo Modules supports and encourages semver versioned modules, and uses the minimal version selection algorithm to resolve versions.
* A new set of CLI commands are provided to manage all of this: `hugo mod init`, `hugo mod get`, `hugo mod graph`, `hugo mod tidy`, and `hugo mod vendor`.
All of the above is backed by Go Modules.
Fixes#5973Fixes#5996Fixes#6010Fixes#5911Fixes#5940Fixes#6074Fixes#6082Fixes#6092
