Adapt existing code to PSR-4

[alombarte]

All code should be converted to make it PSR-4 compliant.
This is (from http://www.php-fig.org/psr/psr-4/):

• The term "class" refers to classes, interfaces, traits, and other similar structures.
  A fully qualified class name has the following form:
  ()*
• The fully qualified class name MUST have a top-level namespace name, also known as a "vendor namespace".
• The fully qualified class name MAY have one or more sub-namespace names.
• The fully qualified class name MUST have a terminating class name.
• Underscores have no special meaning in any portion of the fully qualified class name.
• Alphabetic characters in the fully qualified class name MAY be any combination of lower case and upper case.
• All class names MUST be referenced in a case-sensitive fashion.
• When loading a file that corresponds to a fully qualified class name ...
• A contiguous series of one or more leading namespace and sub-namespace names, not including the leading namespace separator, in the fully qualified class name (a "namespace prefix") corresponds to at least one "base directory".
• The contiguous sub-namespace names after the "namespace prefix" correspond to a subdirectory within a "base directory", in which the namespace separators represent directory separators. The subdirectory name MUST match the case of the sub-namespace names.
• The terminating class name corresponds to a file name ending in .php. The file name MUST match the case of the terminating class name.
• Autoloader implementations MUST NOT throw exceptions, MUST NOT raise errors of any level, and SHOULD NOT return a value.

[lombartec]

Thanks for creating the task, I will have some time this weekend to do this 😄