Add initial support for deflate compression in maxavro

Maxavro now supports reading records with the zlib deflate
algorithm.

With this change, each data block is read into memory in one IO
operation. This allows the library to decompress the data block if
necessary.

The avrorouter does not yet use compression when writing the records.

avro/maxavro_internal.h

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2019-07-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#pragma once
+
+#include "maxavro.h"
+#include <maxscale/alloc.h>
+
+/**
+ * Private header for maxavro
+ */
+
+/** Reading primitives */
+bool maxavro_read_integer(MAXAVRO_FILE *file, uint64_t *val);
+char* maxavro_read_string(MAXAVRO_FILE *file);
+bool maxavro_skip_string(MAXAVRO_FILE* file);
+bool maxavro_read_float(MAXAVRO_FILE *file, float *dest);
+bool maxavro_read_double(MAXAVRO_FILE *file, double *dest);
+
+/** Only used when opening the file */
+bool maxavro_read_integer_from_file(MAXAVRO_FILE *file, uint64_t *val);
+
+/** Reading complex types */
+MAXAVRO_MAP* maxavro_read_map_from_file(MAXAVRO_FILE *file);
+void maxavro_map_free(MAXAVRO_MAP *value);
+
+/**
+ * The following functionality is not yet fully implemented
+ */
+
+/** Schema creation */
+MAXAVRO_SCHEMA* maxavro_schema_alloc(const char* json);
+void maxavro_schema_free(MAXAVRO_SCHEMA* schema);
+
+/** Data block generation */
+MAXAVRO_DATABLOCK* maxavro_datablock_allocate(MAXAVRO_FILE *file, size_t buffersize);
+void maxavro_datablock_free(MAXAVRO_DATABLOCK* block);
+bool maxavro_datablock_finalize(MAXAVRO_DATABLOCK* block);
+
+/** Adding values to a datablock. The caller must ensure that the inserted
+ * values conform to the file schema and that the required amount of fields
+ * is added before finalizing the block. */
+bool maxavro_datablock_add_integer(MAXAVRO_DATABLOCK *file, uint64_t val);
+bool maxavro_datablock_add_string(MAXAVRO_DATABLOCK *file, const char* str);
+bool maxavro_datablock_add_float(MAXAVRO_DATABLOCK *file, float val);
+bool maxavro_datablock_add_double(MAXAVRO_DATABLOCK *file, double val);