Is your feature request related to a problem? Please describe.
Currently it does not seem possible to control serialization of numbers in the library. TOML specification allows numbers to be specified with 0x, 0o, and 0b prefixes. This is a great advantage over other file formats because it allows for serialization of things like hex RGBA color values, Unix permissions, and bitfields/flags in a human-readable format.

Describe the solution you'd like
Implement some way of specifying the number format for insert() and insert_or_assign() methods.

Describe alternatives you've considered
I am not aware of any alternatives.

Additional context
N/A