Comply with the PSR-2 coding style guide

* Rename tests to test
* Run `phpcbf --standard=PSR2 src test`
* Rename TNetstring_Encoder and TNetstring_Decoder to
  \Phuedx\TNetstring\Encoder and \Phuedx\TNetstring\Decoder respectively
* Update the Composer autoloader configuration
* Update the JSON-like API
Migrate to a single codec class

* Add the \Phuedx\TNetstring\Codec class
* Migrate the JSON-like API to use the \Phuedx\TNetstring\Codec class
* Remove the \Phuedx\TNetstring\Encoder and \Phuedx\TNetstring\Decoder
  classes
Update Composer contact deetz
Update the README

* Add the Installation section
* Use the new \Phuedx\TNetstring\Codec class in the Usage section
Merge branch 'develop'