* Accept the format string as Into<String> rather than String to allow
&str to be provided.
* set_colors accepts Into<Vec<TimeColor>> rather than &[TimeColor]. The
function needs a Vec<TimeColor>. Previously it would unconditionally
clone the slice into a Vec, now it can accept a Vec if the user provides
one and avoid an allocation in those cases (while still cloning a slice
if that's what the user provides).
* DateTime::colors was an Option<Vec<TimeColor>> it's now simply a
Vec<TimeColor>. There was no difference in logic between a None and an
empty Vec so the code could be simplified by removing the Option.
* No longer allocate a String when formatting the time.
* Collapse the logic setting color. Calculating whether to set a color
and storing the result in Option<ColorRGB> only to then set data.color
if the Option is Some, can be collapsed to simply set data.color if the
configuration dictates.
