Update README with col_model_for_jqgrid method.
'jqgrid' method renamed to 'to_jqgrid_api' and rewritten.
To provide more flexibility, the method is rewritten.
Chained functions are now supported.
Update README and CHANGELOG files.
Fix url for plugin installation in README file.
Update README file with gem installation.
Add installation instructions to README.rdoc file.
Update README.rdoc file.
Use README.rdoc instead of plain README file.