Add illegal characters handling

Hi, I noticed that when I try to backup data from my Android phones, there is a small numbers of failed items because of errors telling me that filename is invalid. Since UNIX filesystem allow symbols like : or * in file names but Windows don’t, it often causes errors like item "codm\\codm_2019-10-10_12:26:55.png"): syncing: filename is invalid . In which this error often requires manual user followup like renaming or ignoring the file altogether. However, another proprietary sync software called Resilio Sync or formerly known as BTSync can auto correct invalid characters in filename. However this software is feature limited unless paid with 99 dollars annually, and it is not power user optimized. If Syncthing added the feature of handling illegal characters, this would have been better.