python doc: "repl" and "setup-py" are goals now, don't use "py". fix …

…404 link

* rm 'pants py' mentions
* mention `goal repl`, `goal setup-py`
* how to pass args
* show `goal test` in covg section
* fix 404 link
* readability fixes

Testing Done:
rendered at http://pantsbuild.github.io/lahosken-demo/python-readme.html

Bugs closed: 688

Reviewed at https://rbcommons.com/s/twitter/r/1302/

examples/src/python/example/3rdparty_py.md

@@ -27,7 +27,7 @@ file and make a pip `requirements.txt` file in the same directory.
 
 E.g, your `3rdparty/python/BUILD` file might look like:
 
-!inc[start-after=Licensed under&end-before=target](../../../../3rdparty/python/BUILD)
+!inc[start-at=python_requirement&end-before=target](../../../../3rdparty/python/BUILD)
 
 ...with `3rdparty/python/requirements.txt` like:
 
@@ -61,7 +61,7 @@ Your Code's BUILD File
 In your code's `BUILD` file, introduce a dependency on the `3rdparty`
 target:
 
-!inc[start-after=Like Hello](hello/greet/BUILD)
+!inc[start-at=python_library](hello/greet/BUILD)
 
 Then in your Python code, you can `import` from that package:
 

examples/src/python/example/BUILD

@@ -2,6 +2,7 @@ page(
   name='readme',
   source='readme.md',
   links=[
+    ':3rdparty_py',
     ':python_old',
     'src/docs:first_concepts',
   ]

examples/src/python/example/hello/greet/BUILD

@@ -1,8 +1,6 @@
 # Copyright 2014 Pants project contributors (see CONTRIBUTORS.md).
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
-# Like Hello world, but built with Pants.
-
 python_library(name='greet',
   dependencies=[
     '3rdparty/python:ansicolors',