Merge branch 'pr/2'
added symmetric stream cipher
use of stream cipher and refactor 'encrypt' to pass an IV (similar to java)
split AGPBKDF2 in its own class and refactor to be more like the java api
remove AGPBKDF2 generation and refactoring
update testcase to use the new API
added new api headers to the master
xcode project files update
use meaningful name for initialization vector param
use meaningful method name for AGPBKDF2 key generation
added testcase for key length
removed unused constructor
use meaningful name also in the param
initial commit of API documentation
update param to be more clear during check