Refactored string<>bytebuffer conversions to functions in StringUtils and marked todo's for optimizing them.


git-svn-id: http://urho3d.googlecode.com/svn/trunk@2073 3bd170d8-ddcf-f82c-f583-7a401ccf5608
Optimized StringToBuffer & BufferToString.
Fixed warnings in XMLElement.


git-svn-id: http://urho3d.googlecode.com/svn/trunk@2074 3bd170d8-ddcf-f82c-f583-7a401ccf5608