Provide option to use Zopfli

Includes an option to use Zopfli to perform gzip compression. This can
make a small though notable improvement in compression size of the data.
Though can take a bit longer to run. As the data is still gzip
compressed, it can still be decompressed with any gzip implementation
like Pako. So no other changes are needed to handle the data.

Author: jakirkham

nanshe_ipython.ipynb

@@ -1671,6 +1671,9 @@
         "import mmap\n",
         "import textwrap\n",
         "\n",
+        "import zopfli\n",
+        "import zopfli.gzip\n",
+        "\n",
         "import numpy\n",
         "import numpy as np\n",
         "\n",
@@ -1728,7 +1731,8 @@
         "* `roi_alpha` (`float`): transparency of the ROIs in a range of [0.0, 1.0].\n",
         "* `roi_border_width` (`int`): width of the line border on each ROI.\n",
         "* `trace_plot_width` (`int`): width of the trace plot.\n",
-        "* `compresslevel` (`int`): compression level to use with zlib for trace data [0, 9]."
+        "* `compresslevel` (`int`): compression level to use with zlib for trace data [0, 9].\n",
+        "* `use_zopfli` (`bool`): whether to use Zopfli or zlib."
       ]
     },
     {
@@ -1743,6 +1747,7 @@
         "roi_border_width = 3\n",
         "trace_plot_width = 500\n",
         "compresslevel = 6\n",
+        "use_zopfli = False\n",
         "\n",
         "\n",
         "bio.curdoc().clear()\n",
@@ -1821,18 +1826,21 @@
         "    plot_projs.append(plot_std)\n",
         "\n",
         "\n",
-        "def gzip_compress(data, compresslevel=6):\n",
-        "    compressed = io.BytesIO()\n",
-        "    with gzip.GzipFile(fileobj=compressed, mode=\"wb\", compresslevel=compresslevel) as compressor:\n",
-        "        compressor.write(data)\n",
-        "    return compressed.getvalue()\n",
+        "def gzip_compress(data, compresslevel=6, use_zopfli=False):\n",
+        "    if use_zopfli:\n",
+        "        return zopfli.gzip.compress(data, gzip_mode=compresslevel)\n",
+        "    else:\n",
+        "        compressed = io.BytesIO()\n",
+        "        with gzip.GzipFile(fileobj=compressed, mode=\"wb\", compresslevel=compresslevel) as compressor:\n",
+        "            compressor.write(data)\n",
+        "        return compressed.getvalue()\n",
         "\n",
         "\n",
         "all_tr_dtype_srcs = ColumnDataSource(data=dict(traces_dtype=traces.dtype.type(0)[None]))\n",
         "all_tr_shape_srcs = ColumnDataSource(data=dict(traces_shape=traces.shape))\n",
         "all_tr_srcs = ColumnDataSource(data=dict(\n",
         "    traces=numpy.frombuffer(\n",
-        "        gzip_compress(traces.tobytes(), compresslevel=compresslevel),\n",
+        "        gzip_compress(traces.tobytes(), compresslevel=compresslevel, use_zopfli=use_zopfli),\n",
         "        dtype=np.uint8\n",
         "    )\n",
         "))\n",