Update doc for version 1.3.1

changelog, whatsnew
Bump version to 1.3.1
Fix runtime error on deleted cpp obj

(this can happens because the timer call us back just after the
widget has been deleted, while other modes are being uninstalled)
Merge branch 'develop' into develop2

Conflicts:
	pyqode/core/__init__.py
	pyqode/core/modes/filewatcher.py