Update the readme to be specific

It is unlikely that jelly will support other hydrodynamics software in the
future, at least there are no concrete plans to do so.

Should this happen nonetheless, I won't reject such an development. The readme
may be updated at that point but currently I think it is better to reflect the
status quo.
Add the version string to the package

This merely sets the conventional __version__ attribute in the package.
Merge pull request #61 from aepsil0n/version_string

Add the version string to the package
Merge pull request #62 from aepsil0n/update/readme

Update the readme to be specific
Remove tagline from readme file

The tagline is duplicate on both PyPI and GitHub, which does not look nice. In
any case, the information contained should be better conveyed as full text in
the readme.
Merge pull request #63 from aepsil0n/readme_no_tagline

Remove tagline from readme file