Polymake.jl 0.4.0 released

Today Polymake.jl 0.4.0 has been released.

Diff since v0.3.3

Closed issues:

• expose help strings in json files (#192)
• Drop CxxWrap 0.9 support and simplify code again? (#262)

Merged pull requests:

• CxxWrap 0.10.0 (#254) (@benlorenz)
• Just drop julia < 1.3 (#255) (@benlorenz)
• Cleanup and improve CI configuration (#256) (@benlorenz)
• Use CxxWrap.prefix_path (#258) (@fingolfin)
• use official coverage action (#263) (@kalmarek)
• fix/adjust signal handling (#265) (@benlorenz)
• Function docs2 (#266) (@kalmarek)