FILE_ @-code changes/additions

New:
- FILE_COST, file's credit value or "FREE" when applicable
  (see also FILE_CREDITS - the file's credit value or 0 when free download)
- FILE_AUTHOR - file's author (e.g. from SAUCE record) or blank if N/A
- FILE_GROUP - file's author group (e.g. from SAUCE record) or blank if N/A
- FILE_BYTES - file's size in bytes (previously, would use FILE_SIZE for this)
- FILE_CRC32 - 8 hex digits or blank if N/A
- FILE_MD5 - 32 hex digits or blank if N/A
- FILE_SHA1 - 40 hex digits or blank if N/A
- FILE_TIME_TO_DL - estimated time ("HH:MM:SS") to download file at current CPS

Changed:
FILE_SIZE is now the file size estimated in KB, MB, GB, etc., not the exact
file size in bytes.