Add scripts to source distribution using MANIFEST

The setup.py script is programmed to add either scripts/taskplot.cmd or
scripts/taskplot on Windows or Linux respectively. When source
distribution is created on Linux, only scripts/taskplot is included in
the source distribution. Therefore, installation of the program on
Windows fails due to missing scripts/taskplot.cmd. Hence, include both
scripts/taskplot.cmd and scripts/taskplot in the source distribution
irrespective of which system the source distribution to be released is
created on.
Fix scripts' paths in MANIFEST.in inline comments

The inline comments in MANIFEST.in incorrectly mention the scripts
directory as 'script'. It should be 'scripts' instead.
Remove changelog from package long description

The long description of the package is used to create the home
page of the package in PyPI. The changelog looks untidy in the
home page. Therefore, remove it from the long description.
Modify table of contents to make it work on GitHub

ReStructuredText section numbering breaks the links in the
contents on GitHub.  Backlinks do not work on GitHub. Therefore,
remove section numbering as well as backlinks.
Set version number to 0.1.2

Set the module version number to 0.1.2 and add section for this
new version in CHANGES.txt.
Fix issues in README.rst

Fix these two issues in README.rst.

  1. The explanation for task list file based example refers to
     a plural number of files when in fact there is only one
     input file.
  2. The support section requests the user to see the existing
     issues in the issue tracker before posting a new one when
     in fact that the issue tracker is empty right now.