Merge remote-tracking branch 'origin/master'

Conflicts:
	01_01_Phugoid_Theory_sage.pdf
	01_01_Phugoid_Theory_sage.sagews
	01_Phugoid.Theory.Sage/01_01_Phugoid_Theory_sage.pdf
	01_Phugoid.Theory.Sage/01_01_Phugoid_Theory_sage.sagews
	01_Phugoid.Theory.Sage/README.md
	Phugoid.Theory.Sage/01_01_Phugoid_Theory_sage.pdf
	Phugoid.Theory.Sage/01_01_Phugoid_Theory_sage.sagews
	Phugoid.Theory.Sage/README.md
	README-sagews.md