Add /config dir support

This commit adds support for a configuration directory (default `config`). The different pieces in this puzzle are:

* A new `--environment` (or `-e`) flag. This can also be set with the `HUGO_ENVIRONMENT` OS environment variable. The value for `environment` defaults to `production` when running `hugo` and `development` when running `hugo server`. You can set it to any value you want (e.g. `hugo server -e "Sensible Environment"`), but as it is used to load configuration from the file system, the letter case may be important. You can get this value in your templates with `{{ hugo.Environment }}`.
* A new `--configDir` flag (defaults to `config` below your project). This can also be set with `HUGO_CONFIGDIR` OS environment variable.

If the `configDir` exists, the configuration files will be read and merged on top of each other from left to right; the right-most value will win on duplicates.

Given the example tree below:

If `environment` is `production`, the left-most `config.toml` would be the one directly below the project (this can now be omitted if you want), and then `_default/config.toml` and finally `production/config.toml`. And since these will be merged, you can just provide the environment specific configuration setting in you production config, e.g. `enableGitInfo = true`. The order within the directories will be lexical (`config.toml` and then `params.toml`).

```bash
config
├── _default
│   ├── config.toml
│   ├── languages.toml
│   ├── menus
│   │   ├── menus.en.toml
│   │   └── menus.zh.toml
│   └── params.toml
├── development
│   └── params.toml
└── production
    ├── config.toml
    └── params.toml
```

Some configuration maps support the language code in the filename (e.g. `menus.en.toml`): `menus` (`menu` also works) and `params`.

Also note that the only folders with "a meaning" in the above listing is the top level directories below `config`. The `menus` sub folder is just added for better organization.

We use `TOML` in the example above, but Hugo also supports `JSON` and `YAML` as configuration formats. These can be mixed.

Fixes #5422

1 files changed, 9 insertions, 0 deletions

diff --git a/helpers/path.go b/helpers/path.go
index 92b58de84..2d0e8aa64 100644
--- a/helpers/path.go
+++ b/helpers/path.go
@@ -274,6 +274,13 @@ func FileAndExt(in string) (string, string) {
 	return fileAndExt(in, fpb)
 }
 
+// FileAndExtNoDelimiter takes a path and returns the file and extension separated,
+// the extension excluding the delmiter, e.g "md".
+func FileAndExtNoDelimiter(in string) (string, string) {
+	file, ext := fileAndExt(in, fpb)
+	return file, strings.TrimPrefix(ext, ".")
+}
+
 // Filename takes a path, strips out the extension,
 // and returns the name of the file.
 func Filename(in string) (name string) {
@@ -400,6 +407,8 @@ func ExtractRootPaths(paths []string) []string {
 
 }
 
+var numInPathRe = regexp.MustCompile("\\.(\\d+)\\.")
+
 // FindCWD returns the current working directory from where the Hugo
 // executable is run.
 func FindCWD() (string, error) {