Fix typos in comments, docs and test names (#15018)

* Fix typos in comments, docs and test names

* Update test_pyparse.py

account for change in string length

* Apply suggestion: splitable -> splittable

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Apply suggestion: splitable -> splittable

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Apply suggestion: Dealloccte -> Deallocate

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Update posixmodule checksum.

* Reverse idlelib changes.
diff --git a/Doc/library/email.encoders.rst b/Doc/library/email.encoders.rst
index e4752a5..5d68b10 100644
--- a/Doc/library/email.encoders.rst
+++ b/Doc/library/email.encoders.rst
@@ -15,7 +15,7 @@
 This module is deprecated in Python 3.  The functions provided here
 should not be called explicitly since the :class:`~email.mime.text.MIMEText`
 class sets the content type and CTE header using the *_subtype* and *_charset*
-values passed during the instaniation of that class.
+values passed during the instantiation of that class.
 
 The remaining text in this section is the original documentation of the module.