Added auto-sizing to terminal width (if available)

using the "COLUMNS" property of the environment

Fixing up previous commit from out-dated source

I unintentionally added the new feature (auto-size) to an older version
of the code.  This commit re-adds the feature to the current code-base,
and updates the test.jl

Cosmetic changes

Added / fixed comments, cleaned up whitespace.
Changed README to reflect that this is over long running "operations",
not necessarily computations only, and altered the abort message
similarly.   Avoided using "Task" since that has a special meaning in
Julia.

Fixing up tests to head revision

My mistake extended to the test.jl file as well.  Apologies.  I've also
added one more test.

Add import ProgressMeter to test file