[regression] Add dictionary support

Dictionaries are prebuilt and saved as part of the data object.
The config decides whether or not to use the dictionary if it is
available. Configs that require dictionaries are only run with
data that have dictionaries. The method will skip configs that are
irrelevant, so for example ZSTD_compress() will skip configs with
dictionaries.

I've also trimmed the silesia source to 1MB per file (12 MB total),
and added 500 samples from the github data set with a dictionary.

I've intentionally added an extra line to the `results.csv` to make
the nightly build fail, so that we can see how CircleCI reports it.

Full list of changes:

* Add pre-built dictionaries to the data.
* Add `use_dictionary` and `no_pledged_src_size` flags to the config.
* Add a config using a dictionary for every level.
* Add a config that specifies no pledged source size.
* Support dictionaries and streaming in the `zstdcli` method.
* Add a context-reuse method using `ZSTD_compressCCtx()`.
* Clean up the formatting of the `results.csv` file to align columns.
* Add `--data`, `--config`, and `--method` flags to constrain each
  to a particular value. This is useful for debugging a failure
  or debugging a particular config/method/data.

tests/regression/data.h

@@ -22,10 +22,14 @@ typedef enum {
 typedef struct {
     char const* url;   /**< Where to get this resource. */
     uint64_t xxhash64; /**< Hash of the url contents. */
-    char const* name;  /**< The logical name of the resource (no extension). */
-    data_type_t type;  /**< The type of this resource. */
     char const* path;  /**< The path of the unpacked resource (derived). */
-    size_t size;
+} data_resource_t;
+
+typedef struct {
+    data_resource_t data;
+    data_resource_t dict;
+    data_type_t type;  /**< The type of the data. */
+    char const* name;  /**< The logical name of the data (no extension). */
 } data_t;
 
 /**
@@ -33,6 +37,9 @@ typedef struct {
  */
 extern data_t const* const* data;
 
+
+int data_has_dict(data_t const* data);
+
 /**
  * Initializes the data module and downloads the data necessary.
  * Caches the downloads in dir. We add a stamp file in the directory after
@@ -62,7 +69,14 @@ typedef struct {
  *
  * @returns The buffer, which is NULL on failure.
  */
-data_buffer_t data_buffer_get(data_t const* data);
+data_buffer_t data_buffer_get_data(data_t const* data);
+
+/**
+ * Read the dictionary that the data points to into a buffer.
+ *
+ * @returns The buffer, which is NULL on failure.
+ */
+data_buffer_t data_buffer_get_dict(data_t const* data);
 
 /**
  * Read the contents of filename into a buffer.
@@ -88,5 +102,39 @@ int data_buffer_compare(data_buffer_t buffer1, data_buffer_t buffer2);
  */
 void data_buffer_free(data_buffer_t buffer);
 
+typedef struct {
+    char* buffer;
+    char const** filenames;
+    unsigned size;
+} data_filenames_t;
+
+/**
+ * Get a recursive list of filenames in the data object. If it is a file, it
+ * will only contain one entry. If it is a directory, it will recursively walk
+ * the directory.
+ *
+ * @returns The list of filenames, which has size 0 and NULL pointers on error.
+ */
+data_filenames_t data_filenames_get(data_t const* data);
+
+/**
+ * Frees the filenames table.
+ */
+void data_filenames_free(data_filenames_t filenames);
+
+typedef struct {
+    data_buffer_t const* buffers;
+    size_t size;
+} data_buffers_t;
+
+/**
+ * @returns a list of buffers for every file in data. It is zero sized on error.
+ */
+data_buffers_t data_buffers_get(data_t const* data);
+
+/**
+ * Frees the data buffers.
+ */
+void data_buffers_free(data_buffers_t buffers);
 
 #endif