changelog updated

* Modified changelog.txt:

- added two extra changes to psychopy change list
     1) PsychoPy2 IDE stops iohub process when script is terminated by user.

     2) Optional filtering of mouse and keyboard events to only those targeted
at PsychoPy Window. Windows and Linux support only at this time.

- modified textbox comments to reflect current state of code.

* Copied the changed .txt contents to the .rst file (I hope this is how
you do it).

BTW, could the contents of the txt be imported into the rst using a
sphinx command? Then the change log would only need to be updated in one
place.