Issue #1 modernize library

Addresses Issue #1 in the following ways:

Adds in composer support; there is still refinement to be done if the library is hosted through packagist. Documentation has been updated to reflect how the library could be installed through composer. Enforce the library to only be used on PHP 7 or higher.
Use the PSR-2 coding style.
Moves the main search code into a namespace. Documentation has been updated to reflect how to use the library.
Moves the benchmark code into its own class.
Creates a set of phpunit based unit tests.

codeplea / ahocorasickphp