changelog updated

* Modified changelog.txt:

- added two extra changes to psychopy change list
> PsychoPy2 IDE stops iohub process when script is terminated by user.
> 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.
Merge pull request #437 from isolver/master

changelog updated