Adding methods for using shorts with BufferCursor

[slaunay]

It's not possible to read or write short values using the BufferCursor.

Current workaround is to use *WriteByte[s] methods:

 cursor.keyWriteBytes(new byte[] {0, 1});
 cursor.valWriteByte((shortValue >> 8) & 0xff);
 cursor.valWriteByte(shortValue & 0xff);

Code change:

• adding keyWriteShort(short)
• adding keyShort(int)
• adding valWriteShort(short)
• adding valShort(int)
• updating integration tests