ioutil's contents are now in io and os.
Eventually jfa-go's files will be embedded in the binary with go1.16's
new embed feature. Using io/fs will provide abstraction for accessing
these files, and allow for both embedded and non-embedded versions.
Also, internal paths to things like email templates, etc. will be
prefixed with "jfa-go:" to indicate to use the app's own Filesystem
instead of reading the file normally. This also allows for custom files
to continue to be used as they are currently.
