Use "progress logs"/"progress monitors" instead of frontend/backend

Author: tkf

README.md

@@ -1,13 +1,13 @@
-# ProgressLogging: a Logging-based progress bar frontend
+# ProgressLogging: a package for defining progress logs
 
 [![Stable](https://img.shields.io/badge/docs-stable-blue.svg)](https://junolab.github.io/ProgressLogging.jl/stable)
 [![Dev](https://img.shields.io/badge/docs-dev-blue.svg)](https://junolab.github.io/ProgressLogging.jl/dev)
 [![Build Status](https://travis-ci.com/JunoLab/ProgressLogging.jl.svg?branch=master)](https://travis-ci.com/JunoLab/ProgressLogging.jl)
 [![Codecov](https://codecov.io/gh/JunoLab/ProgressLogging.jl/branch/master/graph/badge.svg)](https://codecov.io/gh/JunoLab/ProgressLogging.jl)
 [![Coveralls](https://coveralls.io/repos/github/JunoLab/ProgressLogging.jl/badge.svg?branch=master)](https://coveralls.io/github/JunoLab/ProgressLogging.jl?branch=master)
 
-ProgressLogging.jl is a progress bar _frontend_.  It can be used to
-report progress of a loop/loops with time-consuming body:
+ProgressLogging.jl is a package for defining _progress logs_.  It can
+be used to report progress of a loop/loops with time-consuming body:
 
 ```julia
 julia> using ProgressLogging
@@ -17,9 +17,9 @@ julia> @progress for i in 1:10
        end
 ```
 
-This package is a _frontend_ in the sense using this package alone
-does not show any progress bars.  You need to use one of the backends
-to view the progress.
+This package does not contain any _progress monitors_ for visualizing
+the progress of the program.  You need to install a package supporting
+progress logs created by ProgressLogging.jl API.  For example:
 
 * [Juno](https://junolab.org/)
 * [ProgressMeterLogging.jl](https://github.com/tkf/ProgressMeterLogging.jl)