Release awwan 0.4.0 (2022.02.05)

This release bring new command "serve" to awwan.
The serve command run HTTP server that provide web-user interface to
create, edit, save, and execute script.

===  New features

*  all: implement HTTP API and function to Save file on web-user interface
+
The web-user interface now have button "Save" that save the edited
content of file to storage.

*  all: implement serve command
+
--
The serve command will run a HTTP server that provide web-user interface
to edit and execute script.

Currently, the web-user interface provide the following features,

* Browsing the workspace
* Running the script on local or remote
--

=== Enhancements

*  all: make the local statement executed with "/bin/sh -c ..."
+
By using "sh -c", the statement can contains environment variable,
piping, and other shell commands that cannot be supported if executed
directly using native os.Exec.

*  all: expand the environment on statement when executing local script
+
This changes replace the string ${x} or $x in the statements with the
current environment variables values.
+
For example, statement "mkdir ${HOME}/tmp" will expand the ${HOME} to
the current user home directory.

*  all: use native SFTP to put and get file when possible
+
Previously, the command to put and get file from remote server depends
on installed scp program on the host computer.
+
In this changes we add the SFTP client and use it as primary function
to put and get file to/from remote when possible and use the scp as
fallback.
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