Add an option to only keep latest log statement in terminal

[foster999]

The repeated log statements break up terminal outputs from the process. This may make it difficult to interpret the usual outputs from the process.

An option might be added to specify that only the last log statement should be kept in the terminal output. Previous log statements should be cleaned up as each new log statement is written.

For example:

$ howlong -c python helloworld.py
Running python helloworld.py
INFO:0:00:01.003903
Hello, World!
INFO:0:00:02.005022
Finished python helloworld.py

might become:

$ howlong --latest-only -c python helloworld.py
Running python helloworld.py
Hello, World!
INFO:0:00:02.005022
Finished python helloworld.py