Use a (mostly) hermetic Python interpreter

It still requires python to be installed on the host to run the wrapper
scripts, but it's close to being fully hermetic.

This also requires/enables the following changes, unfortunately all at
the same time:
 * Use a downloaded f2py
 * Use a downloaded scipy/numpy/matplotlib
 * Fix a few things that don't run with the python version in their #!
 * Stop using bazel-generated __init__.py files, because those interfere
   with importing matplotlib nicely

Change-Id: Ife280464613d67cece9587b7d947f0b1d5466d7e
diff --git a/tools/ruby/BUILD b/tools/ruby/BUILD
index 426a9f1..b8b2543 100644
--- a/tools/ruby/BUILD
+++ b/tools/ruby/BUILD
@@ -1,5 +1,5 @@
 py_binary(
-  name = 'standalone_ruby',
-  srcs = ['standalone_ruby.py'],
-  visibility = ['//visibility:public'],
+    name = "standalone_ruby",
+    srcs = ["standalone_ruby.py"],
+    visibility = ["//visibility:public"],
 )