Catch exceptions in logMessage.

NSFileHandle writeData: will throw an exception if any I/O error
occurs.  Catching these means that the app will not crash just
because something went wrong writing a log entry.
No need to include the README.txt file as source file - this generates an XCode warning
Merge pull request #137 from bpoplauschi/noNeedForTxtFile

No need to include the README.txt file as source file - this generates an XCode warning
Merge pull request #130 from tipbit/filelogger-exceptions

Catch exceptions in logMessage.