Adds addition methods to getSections

Adds a method to return all sections found by the parser.

Adds a method to get all the top level sections from the parser.
Top level sections are defined as being either in the format of
1, 2, etc. or 1.0, 2.0, etc.

Adds a method to return all children of a specified section reference.

Adds a method to sort sections by depth and by section order.

Adds methods to Section to calculate their section depth and to
calculate their depth score that assists in ordering sections by
their depth.
Adds get, trim, and belongsToReference to Section

Adds a getReference to Section and chages getSection to call getReference.
Marks getSection as deprecated.

Adds trimReference method to Section that removes any trailing periods
and trims all placeholder zeroes in a section reference. In other words,
3.0.0 is considered to be the same as 3. 3.0.1, of course, remains as
3.0.1.

Adds a method to check if a section is a reference or a child of that
reference. For example, section 2.1.1 would be considered to belong to
reference 2, 2.1, and 2.1.1.

Parser->getSection now throws an UnexpectedValueException if a section
can not be found for the requested reference.

Adds corresponding tests.
Updates example to be more dynamic

Moves all include files to an includes folder. Turns header
and footer into an include file. Moves menu into an include file
and automatically generates menu options by getting all the
topLevelSections from the KSS Parser.

Removes buttons.php and replaces it with a more generic reference.php
file that can be used to render any styleguide section.

Adds another css stylesheet to the project for display section headings
to make the example project have more than one KSS Top Level Section.