Consider special treatment for some types of variables in replace_variables()

[Jeremi360]

I think thatreplace_variables() in some cases should do more that just str(value_of_var).
For example now it makes using Color values need in text needs a workaround.
As str(some_color) returns (0-1, 0-1, 0-1, 0-1) and should #hex_color to be useful.

Like mentioned in Note at Advanced Text Docs:

Current way RDS uses very raw way of converting RakuVars values to strings.
Because of this to use color in text like in example below there is need to use workaround:
GDScript Rakugo.set_variable("test_color", "#" + Color(1, 0.5, 1))

We just need to add special case for Color type and maybe other.