Custom delimiters (#1064)

* frontmatter functions now exported as curried constructors

* changed formats.js to accomodate frontmatter.js changes

* can only use custom delimiters if format is specified

* reverting changes

* updated tests to reflect changes

* created tests for custom delimiters

* updated docs to reflect addition of custom delimiter configuration

* formatByExtension no longer takes custom delimiter

* missed some formatByExtension calls

* Edited the docs according to suggestions

* Throws an error if a custom delimiter is set without declaring frontmatter format

* Throws error if custom delimiter set without explicit and proper frontmatter format being declared

* example config file set to proper defaults

* moved frontmatterFormats to formats

* Update .all-contributorsrc

* updated contributions

* Clarify docs

website/site/content/docs/configuration-options.md

@@ -77,6 +77,7 @@ The `collections` setting is the heart of your Netlify CMS configuration, as it
 - `delete`: `false` prevents users from deleting items in a collection; defaults to `true`
 - `extension`: see detailed description below
 - `format`: see detailed description below
+- `frontmatter_delimiter`: see detailed description under `format`
 - `slug`: see detailed description below
 - `fields` (required): see detailed description below
 
@@ -96,11 +97,11 @@ You may also specify a custom `extension` not included in the list above, as lon
 - `toml`: parses and saves files as TOML-formatted data files; saves with `toml` extension by default
 - `json`: parses and saves files as JSON-formatted data files; saves with `json` extension by default
 - `frontmatter`: parses files and saves files with data frontmatter followed by an unparsed body text (edited using a `body` field); saves with `md` extension by default; default for collections that can't be inferred. Collections with `frontmatter` format (either inferred or explicitly set) can parse files with frontmatter in YAML, TOML, or JSON format. However, they will be saved with YAML frontmatter.
-- `yaml-frontmatter`: same as the `frontmatter` format above, except frontmatter will be both parsed and saved only as YAML, followed by unparsed body text
-- `toml-frontmatter`: same as the `frontmatter` format above, except frontmatter will be both parsed and saved only as TOML, followed by unparsed body text
-- `json-frontmatter`: same as the `frontmatter` format above, except frontmatter will be both parsed and saved as JSON, followed by unparsed body text
+- `yaml-frontmatter`: same as the `frontmatter` format above, except frontmatter will be both parsed and saved only as YAML, followed by unparsed body text. The default delimiter for this option is  `---`.
+- `toml-frontmatter`: same as the `frontmatter` format above, except frontmatter will be both parsed and saved only as TOML, followed by unparsed body text. The default delimiter for this option is  `+++`.
+- `json-frontmatter`: same as the `frontmatter` format above, except frontmatter will be both parsed and saved as JSON, followed by unparsed body text. The default delimiter for this option is  `{` `}`.
 
-The explicit `yaml-frontmatter`, `toml-frontmatter`, and `json-frontmatter` formats above do not currently support custom delimiters. We use `---` for YAML, `+++` for TOML, and `{` `}` for JSON. If a file has frontmatter inside other delimiters it will be included as part of the body text.
+`frontmatter_delimiter`: if you have an explicit frontmatter format declared, this option allows you to specify a custom delimiter like `~~~`.
 
 
 ### `slug`