add find() and find_as<T>()
Minor comment change.
Simplify find() implementation.
Minor comment fix.
Add group array support to parse_stdin.

This gets us back up to two failing tests with the BurntSushi/toml-test
test suite, relating to unicode and escape characters.
Merge find() and find_as() into get() and get_as().

This has a nice side-effect of having all of the get_*() methods work with
fully-qualified keys as well.