Create benchmark for fluent.runtime (fixes #85)

This has a benchmark for imports, one for bundle generation, and
one for a pseudo template.

The data here should inform down-stream consumers what to cache.

Author: Pike

fluent.runtime/tools/benchmarks/README.md

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+To run the benchmarks, do:
+
+    $ pip install -r tools/benchmarks/requirements.txt
+    $ py.test ./tools/benchmarks/fluent_benchmark.py::TestBenchmark --benchmark-warmup=on
+
+To profile the benchmark suite, we recommend py-spy as a
+good tool. Install py-spy: https://github.com/benfred/py-spy
+
+Then do something like this to profile the benchmark. Depending on your
+platform, you might need to use `sudo`.
+
+    $ py-spy -f prof.svg -- py.test ./tools/benchmarks/fluent_benchmark.py::TestBenchmark --benchmark-warmup=off
+
+And look at prof.svg in a browser. Note that this diagram includes the fixture
+setup, warmup and calibration phases which you should ignore.

fluent.runtime/tools/benchmarks/fluent_benchmark.py

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+#!/usr/bin/env python
+# This should be run using pytest
+
+from __future__ import unicode_literals
+
+import sys
+import pytest
+import six
+
+from fluent.runtime import FluentBundle
+
+
+FTL_CONTENT = """
+one = One
+two = Two
+three = Three
+four = Four
+five = Five
+six = Six
+seven = Seven ways to { $destination }
+eight = Eight
+nine = Nine
+ten = Ten
+"""
+
+@pytest.fixture
+def fluent_bundle():
+    ctx = FluentBundle(['pl'], use_isolating=False)
+    ctx.add_messages(FTL_CONTENT)
+    return ctx
+
+
+def fluent_template(bundle):
+    return (
+        "preface" +
+        bundle.format("one")[0] +
+        bundle.format("two")[0] +
+        bundle.format("three")[0] +
+        bundle.format("four")[0] +
+        bundle.format("five")[0] +
+        bundle.format("six")[0] +
+        bundle.format("seven", {"destination": "Mars"})[0] +
+        bundle.format("eight")[0] +
+        bundle.format("nine")[0] +
+        bundle.format("ten")[0] +
+        "tail"
+    )
+
+
+class TestBenchmark(object):
+    def test_template(self, fluent_bundle, benchmark):
+        result = benchmark(lambda: fluent_template(fluent_bundle))
+
+    def test_bundle(self, benchmark):
+        def test_bundles():
+            FluentBundle(['pl'], use_isolating=False)
+            FluentBundle(['fr'], use_isolating=False)
+        benchmark(test_bundles)
+
+    def test_import(self, benchmark):
+        def test_imports():
+            # prune cached imports
+            fluent_deps = [
+                k for k in sys.modules.keys()
+                if k.split('.', 1)[0] in ('babel','fluent','pytz')
+            ]
+            for k in fluent_deps:
+                del sys.modules[k]
+            from fluent.runtime import FluentBundle  # noqa
+        benchmark(test_imports)

fluent.runtime/tools/benchmarks/requirements.txt

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+pytest
+pytest-benchmark