Add HPACK test cases

fixtures/hpack/README.md

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+# hpack-test-case
+
+## Spec
+
+HPACK: Header Compression for HTTP/2
+https://tools.ietf.org/html/rfc7541
+
+
+## Directory
+
+The ```raw-data``` directory has original stories of header data in
+json.
+
+Other than ```raw-data``` directory, the HPACK implementations have
+their own directories to store the result of its encoder.
+
+You can perform interoperability testing for your implementation with
+them.
+
+## File Name
+
+Each json in story-#{n}.json is story case and shares compression
+context. Each story is either series of requests or responses.
+
+## JSON Format
+
+Each json has:
+
+- description: general description of encoding strategy or implementation.
+- cases: array of test cases.
+  - seqno: a sequence number. 0 origin.
+  - header_table_size: the header table size sent in SETTINGS_HEADER_TABLE_SIZE and ACKed just before this case. The first case should contain this field. If omitted, the default value, 4,096, is used.
+  - wire: encoded wire data in hex string.
+  - headers: decoded http header in hash.
+
+To test the decoder implementation, for each story file, for each case
+in ```cases``` in the order they appear, decode compressed header
+block in ```wire``` and verify the result against the header set in
+```headers```. Please note that elements in ```cases``` share the same
+compression context.
+
+To test the encoder implementation, generate json story files by
+encoding header sets in ```headers```. Using json files in
+```raw-data``` is handy. Then use your decoder to verify that it can
+successfully decode the compressed header block. If you can play with
+other HPACK decoder implementations, try decoding your encoded data
+with them. If there is any mismatch, then there must be a bug in
+somewhere either encoder or decoder, or both.
+
+```js
+{
+  "description": "Encoded request headers with Literal without index only.",
+  "cases": [
+    {
+      "seqno": 0,
+      "header_table_size": 4096,
+      "wire": "1234567890abcdef",
+      "headers": [
+        { ":method": "GET" },
+        { ":scheme": "http" },
+        { ":authority": "example.com" },
+        { ":path": "/" },
+        { "x-my-header": "value1,value2" }
+      ]
+    },
+    .....
+  ]
+}
+```
+
+## Original Data
+
+These Header Data are converted from https://github.com/http2/http_samples
+
+
+## Compression Ratio
+
+https://github.com/http2jp/hpack-test-case/wiki/Compression-Ratio
+
+
+## Contributor
+
+- jxck
+- summerwind
+- kazu-yamamoto
+- tatsuhiro-t
+
+
+## License
+
+The MIT License (MIT)