Update TODO

Include feature requests requested in #26, as well as others received
via email.
PID file

Write PID file when running in background and specified in configuration
file.
Update bench_sniproxy

Allow overwriting ports via environmental variables and specifying
wrappers such as strace and valgrind for sniproxy like functional_test
allows.
Initialize struct msghdr by hand

Avoids C90 warnings.
Fix signed and unsigned compare
Include stdio.h for size_t
Remove debug syslog messages on backend matching
Merge branch 'master' into libev

Conflicts:
	TODO