v0.4.0

DisjunctiveProgramming v0.4.0

Diff since v0.3.6

Merged pull requests:

• merge https://github.com/pulsipher/DisjunctiveProgramming.jl/tree/str… (#68) (@hdavid16)

Closed issues:

• Interval arithmetic can't be applied to quadratic constraints to insert big M value (#62)
• Fix propositions in paper example (#63)