yaml: implement basic Swagger/OpenAPI subparser

The parser is able to parse both Swagger 2.0 and Openapi 3.0.x.
The code is partly based on ansible playbook parser.  It was tested
using the following vim's TagBar parser declaration:

    let g:tagbar_type_yaml = {
                        \  'ctagstype': 'openapi',
                        \  'kinds': [
                        \          'p:path',
                        \          'd:schema',
                        \          'P:parameter',
                        \          'R:response',
                        \          ]
                        \ }

Tmain/list-subparsers-all.d/stdout-expected.txt

@@ -10,6 +10,7 @@ IPythonCell          Python     base => sub {shared}
 ITcl                 Tcl        base <> sub {bidirectional}
 Maven2               XML        base <> sub {bidirectional}
 Moose                Perl       base <> sub {bidirectional}
+OpenApi              Yaml       base <> sub {bidirectional}
 PlistXML             XML        base <> sub {bidirectional}
 PythonLoggingConfig  Iniconf    base <> sub {bidirectional}
 QtMoc                C++        base <> sub {bidirectional}

Units/parser-openapi.r/openapi.d/args.ctags

@@ -0,0 +1 @@
+--language-force=openapi

Units/parser-openapi.r/openapi.d/expected.tags

@@ -0,0 +1,7 @@
+/sample/other/path	input.yaml	/^    \/sample\/other\/path:$/;"	p
+/sample/path	input.yaml	/^    \/sample\/path:$/;"	p
+CustomHeader	input.yaml	/^        CustomHeader:$/;"	P
+NullableField	input.yaml	/^        NullableField:$/;"	d
+NullableFieldStringEnum	input.yaml	/^        NullableFieldStringEnum:$/;"	d
+Response1	input.yaml	/^        Response1:$/;"	R
+Response2	input.yaml	/^        Response2:$/;"	R

Units/parser-openapi.r/openapi.d/features

@@ -0,0 +1 @@
+yaml

Units/parser-openapi.r/openapi.d/input.yaml

@@ -0,0 +1,55 @@
+openapi: 3.0.0
+info:
+    title: test
+    description: test
+    version: '1.0'
+
+servers:
+  - url: http://example.com
+    description: production
+
+paths:
+    /sample/path:
+        get:
+            summary: simple handler
+            responses: {}
+
+    /sample/other/path:
+        get:
+            responses: {}
+        post:
+            summary: xxx
+            responses: {}
+
+components:
+    schemas:
+        NullableField:
+            type: object
+            properties: {}
+        NullableFieldStringEnum:
+            type: object
+            properties: {}
+
+    parameters:
+        CustomHeader:
+            in: header
+            name: X-Custom-Header
+            required: false
+            schema:
+                type: string
+
+    responses:
+        Response1:
+            description: Payment Required
+            content:
+                application/json:
+                    schema:
+                        type: object
+                        properties: {}
+        Response2:
+            description: smth 2
+            content:
+                application/json:
+                    schema:
+                        type: object
+                        properties: {}

Units/parser-openapi.r/swagger.d/args.ctags

@@ -0,0 +1 @@
+--language-force=openapi

Units/parser-openapi.r/swagger.d/expected.tags

@@ -0,0 +1,8 @@
+/sample/other/path	input.yaml	/^    \/sample\/other\/path:$/;"	p
+/sample/path	input.yaml	/^    \/sample\/path:$/;"	p
+Param1	input.yaml	/^    Param1:$/;"	P
+Param2	input.yaml	/^    Param2:$/;"	P
+PolymorphicInteger	input.yaml	/^    PolymorphicInteger:$/;"	d
+PolymorphicString	input.yaml	/^    PolymorphicString:$/;"	d
+Response1	input.yaml	/^    Response1:$/;"	R
+Response2	input.yaml	/^    Response2:$/;"	R

Units/parser-openapi.r/swagger.d/features

@@ -0,0 +1 @@
+yaml

Units/parser-openapi.r/swagger.d/input.yaml

@@ -0,0 +1,64 @@
+swagger: '2.0'
+info:
+    description: test
+    title: test
+    version: '1.0'
+host: example.com
+
+paths:
+    /sample/path:
+        post:
+            description: test
+            responses:
+              200:
+                description: xxx
+
+    /sample/other/path:
+        get:
+            description: smth
+            responses:
+              200:
+                description: xxx
+
+definitions:
+    PolymorphicString:
+        type: object
+        required:
+          - type
+          - value
+        additionalProperties: false
+        properties:
+            type:
+                type: string
+            value:
+                type: string
+
+    PolymorphicInteger:
+        type: object
+        required:
+          - type
+          - value
+        additionalProperties: false
+        properties:
+            type:
+                type: string
+            value:
+                type: integer
+
+parameters:
+    Param1:
+        name: test1
+        in: query
+        type: boolean
+
+    Param2:
+        name: test2
+        in: query
+        type: boolean
+
+responses:
+    Response1:
+        description: aaa
+
+    Response2:
+        description: bbb

docs/news.rst

@@ -439,6 +439,7 @@ The following parsers have been added:
 * M4
 * NSIS
 * ObjectiveC
+* OpenAPI 3.x.x / Swagger 2.0
 * Passwd *optlib*
 * PuppetManifest *optlib*
 * Perl6

main/parsers_p.h

@@ -29,7 +29,8 @@
 #ifdef HAVE_LIBYAML
 #define YAML_PARSER_LIST						\
 	YamlParser,									\
-	AnsiblePlaybookParser
+	AnsiblePlaybookParser, \
+	OpenApiParser
 #else
 #define YAML_PARSER_LIST
 #endif