Revert "Fixed syntax of fixity declarations."

This reverts commit 07ab0fa052843dc8fd4c874876d03d8a71525f87.
Revert "Added fixity declarations for member, notMember, union, and intersection."

This reverts commit 3999b512f5aa28a7b119a18b286a8485d1285319.
Added fixity declarations for member, notMember, union, and intersection.
Fixed syntax of fixity declarations.
Merge branch 'selinger-master' into develop.

PVP: Major version bump is needed.
Make types of the drawing functions more generic, i.e. Show s => Tree s instead of Tree String
Merge branch 'jonasc-master' into develop

PVP: Major version bump is needed.