add the config option to store files in random sub directories

fixed "Implicitly marking parameter as nullable is deprecated"

added PHP 8.1 ArrayAccess/Iterator/Countable compatibility

remove the fallback for mime type detected, too error prone. closes #18

fixed missing destination path check

incorrect indentation causes the file to be skipped; related #12

only attempt to delete temp file when it was created; closes #11

make sure isValid is updated after the file move

only delete when the file created was a temp file. Closes fuel/core#1544

Tagging the code for 1.7, so we can pin composer to it for the 1.x co…

…debase