Use random ports when port number is 0

[ekzhang]

With this pull request, we no longer use bind("0.0.0.0", 0) from the operating system to choose an arbitrary available port. Instead, we use our own random number generator and retry 150 times. See comments for an explanation of where this constant comes from.

• Resolves Min port is not respected for randomly assigned ports #70
• Resolves Bug(?)/Feature Request: "new client port" is always zero. Print Port of Connected Machines? #75
• Closes Change server behavior when port by local is set to 0 #28

[ekzhang]

Merging this will be a minor version update, to v0.5.0, since I changed some of the library method signatures.