v0.8.1

v0.8.1 (2020-03-02)

Diff since v0.8.0

Merged pull requests:

• add pretty printing infrastructure (#578) (fieker)
• direct sum modules (#574) (fieker)
• Replace obsolete cdn.mathjax.org (#573) (fingolfin)
• Clarify that Julia 1.0 is required (#568) (fingolfin)
• two problems _map and check_parent (#565) (fieker)
• map_coeffs: do not map on zero coeffs (as per docstring) (#562) (rfourquet)