Add Subparser alias names support

The alias names can be set for Subparser using Subparser#aliases().
Make return type concrete class for internal classes

This will make tests eaiser.
Document Subparser#aliases() in usage.apt
Update README.rst
Use StringBuilder instead of StringBuffer
Insert spaces in the middle of the help message to  make them look nicer

Simple hack to make help message look like groff output.
Fix last short option in concatenated form does not consume next argument

If -1 does not consume argument and -2 does, in the old implementation,
command line "-12 foo" does not parse because -2 is assumed to take
empty string as an argument and foo is unrecognized argument.
With this change, -2 correctly takes foo as an argument.
Use charAt instead of substring when extracting 1 character
[maven-release-plugin] prepare release argparse4j-0.3.2
[maven-release-plugin] prepare for next development iteration
Update site
Update NEWS
Correct download link