Validate format patterns when parsing the configuration

[plannigan]

Is your feature request related to a problem? Please describe.
When reading the configuration file, the only validation that happens for format patterns is ensuring they are strings. However, there are a number of issues that can exist in that string. These errors are caught at run time, but it might be possible to catch them earlier.

Describe the solution you'd like
Have a mechanism for checking that the format pattern does not reference invalid keys or is somehow invalidly structured before attempting to use it.