Add support for generating snippets in Markdown

This commit introduces support for generating snippets formatted
using Markdown. Asciidoctor remains the default.

A new SnippetFormat abstraction has been introduced with Asciidoctor
and Markdown implementations provided out of the box.
Markdown-formatted templates are also provided for all of the default
snippets.

Please refer to the updated reference documentation for further
details.

Closes gh-150
Closes gh-19

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/curl-request-with-title.snippet

@@ -0,0 +1,4 @@
+{{title}}
+```bash
+$ curl {{url}} {{options}}
+```

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/http-request-with-title.snippet

@@ -0,0 +1,8 @@
+{{title}}
+```http
+{{method}} {{path}} HTTP/1.1
+{{#headers}}
+{{name}}: {{value}}
+{{/headers}}
+{{requestBody}}
+```

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/http-response-with-title.snippet

@@ -0,0 +1,8 @@
+{{title}}
+```http
+HTTP/1.1 {{statusCode}} {{statusReason}}
+{{#headers}}
+{{name}}: {{value}}
+{{/headers}}
+{{responseBody}}
+```

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/links-with-extra-column.snippet

@@ -0,0 +1,5 @@
+Relation | Description | Foo
+-------- | ----------- | ---
+{{#links}}
+{{rel}} | {{description}} | {{foo}}
+{{/links}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/links-with-title.snippet

@@ -0,0 +1,6 @@
+{{title}}
+Relation | Description
+-------- | -----------
+{{#links}}
+{{rel}} | {{description}}
+{{/links}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/path-parameters-with-extra-column.snippet

@@ -0,0 +1,5 @@
+Parameter | Description | Foo
+--------- | ----------- | ---
+{{#parameters}}
+{{name}} | {{description}} | {{foo}}
+{{/parameters}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/path-parameters-with-title.snippet

@@ -0,0 +1,6 @@
+{{title}}
+Parameter | Description
+--------- | -----------
+{{#parameters}}
+{{name}} | {{description}}
+{{/parameters}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/request-fields-with-extra-column.snippet

@@ -0,0 +1,5 @@
+Path | Type | Description | Foo
+---- | ---- | ----------- | ---
+{{#fields}}
+{{path}} | {{type}} | {{description}} | {{foo}}
+{{/fields}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/request-fields-with-title.snippet

@@ -0,0 +1,6 @@
+{{title}}
+Path | Type | Description
+---- | ---- | -----------
+{{#fields}}
+{{path}} | {{type}} | {{description}}
+{{/fields}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/request-headers-with-extra-column.snippet

@@ -0,0 +1,5 @@
+Name | Description | Foo
+---- | ----------- | ---
+{{#headers}}
+{{name}} | {{description}} | {{foo}}
+{{/headers}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/request-headers-with-title.snippet

@@ -0,0 +1,6 @@
+{{title}}
+Name | Description
+---- | -----------
+{{#headers}}
+{{name}} | {{description}}
+{{/headers}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/request-parameters-with-extra-column.snippet

@@ -0,0 +1,5 @@
+Parameter | Description | Foo
+--------- | ----------- | ---
+{{#parameters}}
+{{name}} | {{description}} | {{foo}}
+{{/parameters}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/request-parameters-with-title.snippet

@@ -0,0 +1,6 @@
+{{title}}
+Parameter | Description
+--------- | -----------
+{{#parameters}}
+{{name}} | {{description}}
+{{/parameters}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/response-fields-with-extra-column.snippet

@@ -0,0 +1,5 @@
+Path | Type | Description | Foo
+---- | ---- | ----------- | ---
+{{#fields}}
+{{path}} | {{type}} | {{description}} | {{foo}}
+{{/fields}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/response-fields-with-title.snippet

@@ -0,0 +1,6 @@
+{{title}}
+Path | Type | Description
+---- | ---- | -----------
+{{#fields}}
+{{path}} | {{type}} | {{description}}
+{{/fields}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/response-headers-with-extra-column.snippet

@@ -0,0 +1,5 @@
+Name | Description | Foo
+---- | ----------- | ---
+{{#headers}}
+{{name}} | {{description}} | {{foo}}
+{{/headers}}

spring-restdocs-core/src/test/resources/custom-snippet-templates/md/response-headers-with-title.snippet

@@ -0,0 +1,6 @@
+{{title}}
+Name | Description
+---- | -----------
+{{#headers}}
+{{name}} | {{description}}
+{{/headers}}