Release exfat 5.8.1 version

• Bug fixes

  • Fix memory leak on mount failure with iocharset= option.
  • Fix Incorrect update of stream entry.
  • Fix cluster range validation error.

• Clean-up codes

  • Remove unused code and unneeded assignment.
  • Rename variables in exfat structure as specification.
  • Reorganize boot sector analysis code.
  • Simplify exfat_utf8_d_hash and exfat_utf8_d_cmp().
  • Optimize exfat entry cache functions.
  • Improve wording of EXFAT_DEFAULT_IOCHARSET config option.

• New Feature

  • Add boot region verification.