add path function to work the same as the asset function

the difference between those 2 functions is
assets always starts from the public/ while asset takes a full path
starting from the app/
update the tests

to affect this commit 6a0ed63b22c20e3117c4e35c8b2f35e8926b4ccf changes
update the readme file
refactor class CdnFacade

rename preparePathAndCallUrlGenerator to generateUrl
and update this function parameter

related to commit #6a0ed63b22c20e3117c4e35c8b2f35e8926b4ccf
refactor test CdnFacadeTest

rename testPreparePathThrowsExceptionWhenEmptyParameter to
testUrlGeneratorThrowsException

related to commit #6a0ed63b22c20e3117c4e35c8b2f35e8926b4ccf
refactor CdnFacade

related to commit #6a0ed63b22c20e3117c4e35c8b2f35e8926b4ccf
fix the test after refactoring the CdnFacade

related to commit #6a0ed63b22c20e3117c4e35c8b2f35e8926b4ccf
Merge pull request #21 from Vinelab/update/add-path-function

add a path() function