new function vfs_unlink(): removes a file
vfs_sd_unlink implementation
ECMD "rm" to delete a file on SD card
finally inlucde vfs_sd_unlink in VFS_SD_FUNCS
Merge pull request #241 from eku/vfs_unlink

Vfs unlink
New option to log any received ECMD via SYSLOG
reformat file to comply with Ethersex's style guide
use uip_buf to collect the data
closes http://bugs.ethersex.de/view.php?id=23
Merge pull request #242 from eku/dyndns

DYNDNS
restructuring of I/O config menu