Get rid of iconv, collation now is reasonably fast

lib/ffi-icu/uchar.rb

@@ -1,10 +1,10 @@
-require 'iconv'
-
 module ICU
 
   class UCharPointer < FFI::MemoryPointer
     def self.from_string(str)
-      super Iconv.conv("wchar_t", "utf-8", str.encode("UTF-8"))
+      # not sure how this will work with other encodings
+      str = str.encode("UTF-8") if str.respond_to? :encode
+      super str.unpack("U*").pack("L*")
     end
   end