Add configuration for running tests on Travis CI
Fix starting and stopping of nksip_counters in test

Previously, `exit(Pid, normal)` would not actually kill the
gen_server.
Clarify references to ets table and server name in nksip_counters

These helper macros makes the purpose of the module name clearer in
their respective contexts.
Merge pull request #5 from danielwhite/travis

Provide support for building tests on travis