Don't specify a Ruby version
Allow SIPp sender IP to be unset

This will make SIPp attempt to auto-determine the correct source IP and interface. It’s not guaranteed to work, but since it *can* work, we should permit it.
Don’t attempt cleanup if there is nothing to clean

This can happen if an exception occurs before the temp files are written
Attempt to preserve screen trace
Move screen file locating to sipp

Relies on sipp/sipp#106
Documentation
Spec for screen_file
Officially support 2.0.0 and 2.1.0
Merge pull request #68 from mojolingo/feature/save_screen_trace

Preserve screen trace files on request
Organization: keep like tests together
Support for saving `-trace_err`
Changes
Add rate increase options
Rename max_concurrent to be consistent with CPS
Document default value
Merge pull request #69 from mojolingo/feature/linear_cps_increase

Feature: Linear cps increase
Handle multiple arguments to methods in YAML
Merge pull request #70 from mojolingo/feature/yaml_method_args

Handle multiple arguments to methods in YAML
Write PCAP file in binary mode
Merge pull request #46 from mojolingo/feature/binary-pcap-file

Write PCAP file in binary mode