PEP 219: Fix grammatical mistakes (#900)

pep-0219.txt

@@ -25,7 +25,7 @@ implementation, they do not regard Stackless as a reference
 implementation.  Stackless (with an extension module) implements
 continuations, and from continuations one can implement
 coroutines, microthreads (as has been done by Will Ware [2]_) and
-generators. But in more that a year, no one has found any other
+generators. But in more than a year, no one has found any other
 productive use of continuations, so there seems to be no demand
 for their support.
 
@@ -54,7 +54,7 @@ simple case of coroutines.)
 Real threads allocate a full-sized stack for each thread of
 control, and this is the major source of overhead. However,
 coroutines and microthreads can be implemented in Python in a way
-that involves almost no overhead.  This PEP, therefor, offers a
+that involves almost no overhead.  This PEP, therefore, offers a
 way for making Python able to realistically manage thousands of
 separate "threads" of activity (vs. today's limit of perhaps dozens
 of separate threads of activity).
@@ -158,7 +158,7 @@ itself.
 
 Most recursions of the interpreter are not this complex, but
 fairly frequently, some "post" operations are required. Stackless
-does not fix these situations because of amount of code changes
+does not fix these situations because of the amount of code changes
 required. Instead, Stackless prohibits transfers out of a nested
 interpreter. While not ideal (and sometimes puzzling), this
 limitation is hardly crippling.