Create obstacle avoidance node

[mbr4477]

Accepts structured obstacle data and ideal navigation Twist, and outputs a modified Twist influenced by the obstacles.

[mbr4477]

Same as #7 , I think @irowebbn has this code locally, but it needs pushed to a branch here. Leaving open since this feature has not yet been merged into master.

[irowebbn]

A draft of this was added with ca93ee2, but I haven't had a chance to actually test the obstacle avoidance portion of this code. Trying to figure out a way to test this effectively.