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
The main item in this commit is showing of errors with a file context when running `hugo server`.
This can be turned off: `hugo server --disableBrowserError` (can also be set in `config.toml`).
But to get there, the error handling in Hugo needed a revision. There are some items left TODO for commits soon to follow, most notable errors in content and config files.
Fixes#5284Fixes#5290
See #5325
See #5324
