Deprecate marshalUri properly
Deprecate marshalUri properly

- Added getHeader() static method for doing case-insensitive fetching of
  headers; values are comma-concatenated, allowing for safe lookups and
  consistent return values. This allows removal of marshalUri() in the future,
  and, for the short-term, having it proxy to marshalUriFromServer().

mnapoli/zend-diactoros,localheinz/zend-diactoros,jguittard/zend-diactoros,Ocramius/zend-diactoros,Maks3w/zend-diactoros,deepfreeze/zend-diactoros,mtymek/zend-diactoros