Update partial_doc.md (#308)

Clean up the docs to make them look significantly better.

No semantics changes, just styling.

docs/partial_doc.md

@@ -12,16 +12,22 @@ passed to it at the call sites.
 A partial 'function' can be defined with positional args and kwargs:
 
   # function with no args
+  ```
   def function1():
     ...
+  ```
 
   # function with 2 args
+  ```
   def function2(arg1, arg2):
     ...
+  ```
 
   # function with 2 args and keyword args
+  ```
   def function3(arg1, arg2, x, y):
     ...
+  ```
 
 The positional args passed to the function are the args passed into make
 followed by any additional positional args given to call. The below example
@@ -29,24 +35,30 @@ illustrates a function with two positional arguments where one is supplied by
 make and the other by call:
 
   # function demonstrating 1 arg at make site, and 1 arg at call site
+  ```
   def _foo(make_arg1, func_arg1):
-  print(make_arg1 + " " + func_arg1 + "!")
+    print(make_arg1 + " " + func_arg1 + "!")
+  ```
 
 For example:
 
+  ```
   hi_func = partial.make(_foo, "Hello")
   bye_func = partial.make(_foo, "Goodbye")
   partial.call(hi_func, "Jennifer")
   partial.call(hi_func, "Dave")
   partial.call(bye_func, "Jennifer")
   partial.call(bye_func, "Dave")
+  ```
 
 prints:
 
+  ```
   "Hello, Jennifer!"
   "Hello, Dave!"
   "Goodbye, Jennifer!"
   "Goodbye, Dave!"
+  ```
 
 The keyword args given to the function are the kwargs passed into make
 unioned with the keyword args given to call. In case of a conflict, the
@@ -56,29 +68,34 @@ value for keyword arguments and override it at the call site.
 Example with a make site arg, a call site arg, a make site kwarg and a
 call site kwarg:
 
+  ```
   def _foo(make_arg1, call_arg1, make_location, call_location):
     print(make_arg1 + " is from " + make_location + " and " +
           call_arg1 + " is from " + call_location + "!")
 
   func = partial.make(_foo, "Ben", make_location="Hollywood")
   partial.call(func, "Jennifer", call_location="Denver")
-
+  ```
+  
 Prints "Ben is from Hollywood and Jennifer is from Denver!".
 
+  ```
   partial.call(func, "Jennifer", make_location="LA", call_location="Denver")
-
+  ```
+  
 Prints "Ben is from LA and Jennifer is from Denver!".
 
 Note that keyword args may not overlap with positional args, regardless of
 whether they are given during the make or call step. For instance, you can't
 do:
 
+```
 def foo(x):
   pass
 
 func = partial.make(foo, 1)
 partial.call(func, x=2)
-
+```
 
 ### Parameters