fn tests: functional test framework

make test-functional - runs our tests
run_tests.sh - a harness that runs all other test_*.sh tests
test.inc.sh - common code and functions for tests
fn tests: document writing functional tests
fn tests: enable testing on Travis
fn tests: pocount no args
fn tests: pocount -h test
fn tests: pocount of single po file
fn tests: pocount mutually exclusive options
fn tests: pofilter listfilters
fn tests: pofilter --manpage
fn tests: prop2po no param
fn tests: prop2po simple file conversion
fn tests: prop2po processing directories
fn tests: pocount non-existant file
fn tests: prop2po with templates
fn tests: Add a TODO list

This is a list of all tools that we probably need to test in our
coverage.