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 + "!")
+  ```
 
 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
@@ -56,16 +68,20 @@ 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!".
 
@@ -73,12 +89,13 @@ 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