Fix some minor typos/formatting

pep-3107.txt

@@ -25,7 +25,7 @@ Rationale
 
 Because Python's 2.x series lacks a standard way of annotating a
 function's parameters and return values (e.g., with information about
-a what type a function's return value should be), a variety of tools
+what type a function's return value should be), a variety of tools
 and libraries have appeared to fill this gap [#tailexamp]_.  Some
 utilise the decorators introduced in "PEP 318", while others parse a
 function's docstring, looking for annotations there.
@@ -69,14 +69,14 @@ what annotations are and are not:
    Another library might be used to provide typechecking for Python
    functions and methods.  This library could use annotations to
    indicate the function's expected input and return types, possibly
-   something like ::
+   something like::
 
         def haul(item: Haulable, *vargs: PackAnimal) -> Distance:
             ...
 
    However, neither the strings in the first example nor the
    type information in the second example have any meaning on their
-   own;  meaning comes from third-party libraries alone.
+   own; meaning comes from third-party libraries alone.
 
 3. Following from point 2, this PEP makes no attempt to introduce
    any kind of standard semantics, even for the built-in types.
@@ -99,7 +99,7 @@ Parameters
 
 Annotations for parameters take the form of optional expressions that
 follow the parameter name.  This example indicates that parameters 'a'
-and 'c' should both be a ``Number``, while parameter 'b' should both
+and 'c' should both be a ``Number``, while parameter 'b' should
 be a ``Mapping``::
 
     def foo(a: Number, b: Mapping, c: Number = 5):
@@ -149,8 +149,7 @@ The parameter list can now be followed by a literal ``->`` and a
 Python expression.  Like the annotations for parameters, this
 expression will be evaluated when the function definition is executed.
 
-The grammar for function definitions [#grammar]_ is now something like
-::
+The grammar for function definitions [#grammar]_ is now something like::
 
     funcdef         ::=     [decorators] "def" funcname "("
                             [parameter_list] ")" ["->" expression] ":" suite