also redownload if the file on disk is larger
change redownload threshold
use keyword arg in iter_content

Conflicts:
	courseradownloader/courseradownloader.py
prepare for 2.0 release
properly respect mppl, even for filenames, fixes #124

Conflicts:
	courseradownloader/courseradownloader.py
bump version
Address #134
Conflicts:
	courseradownloader/courseradownloader.py
bump version
Bump version & update changelog