Expanded Usage docs and added Usage examples

* Modified usage to show step-by-step usage in a simple and advanced manner.
* While rewriting usage documenation, made two attributes (elitism,
  maximum_fitness) of the Genetic Algorithm class parameter values passed to
  the __init__ method of the GA class.
Documentation modifications

* Removed ‘search’ page from documentation.
* Moved ‘examples’ section out from Usage and into its own section.
* Changed ‘Simple usage’ and ‘Advanced usage’ to just ‘Simple’ and ‘Advanced’
  in docs/usage.rst
Added recent changes to HISTORY
Update to version v0.2.5
Merge branch 'release/v0.2.5' into develop