Port FlatBuffers to Python.

Implement code generation and self-contained runtime library for Python.

The test suite verifies:
  - Correctness of generated Python code by comparing output to that of
    the other language ports.
  - The exact bytes in the Builder buffer during many scenarios.
  - Vtable deduplication correctness.
  - Edge cases for table construction, via a fuzzer derived from the Go
    implementation.
  - All code is simultaneously valid in Python 2.6, 2.7, and 3.4.

The test suite includes benchmarks for:
  - Building 'gold' data.
  - Parsing 'gold' data.
  - Deduplicating vtables.

All tests pass on this author's system for the following Python
implementations:
  - CPython 2.6.7
  - CPython 2.7.8
  - CPython 3.4.2
  - PyPy 2.5.0 (CPython 2.7.8 compatible)

python/flatbuffers/compat.py

@@ -0,0 +1,27 @@
+""" A tiny version of `six` to help with backwards compability. """
+
+import sys
+
+PY2 = sys.version_info[0] == 2
+PY26 = sys.version_info[0:2] == (2, 6)
+PY3 = sys.version_info[0] == 3
+PY34 = sys.version_info[0:2] >= (3, 4)
+
+if PY3:
+    string_types = (str,)
+    binary_type = bytes
+    range_func = range
+    memoryview_type = memoryview
+    struct_bool_decl = "?"
+else:
+    string_types = (basestring,)
+    binary_type = str
+    range_func = xrange
+    if PY26:
+        memoryview_type = buffer
+        struct_bool_decl = "<b"
+    else:
+        memoryview_type = memoryview
+        struct_bool_decl = "?"
+
+# NOTE: Future Jython support may require code here (look at `six`).