Space handling in kwargs output

[Arkoniak]

As it was mentioned in #19 (comment) by default logger does not print space between message and keyword arguments:

julia> with_logger(MiniLogger()) do
       @info "hello" x=4 y=2
       end
[2022-04-29 10:55:19] Info: hellox = 4, y = 2

Relevant piece of code is: https://github.com/JuliaLogging/MiniLoggers.jl/blob/master/src/minilogger.jl#L242-L253

Proper behavior should be:

julia> with_logger(MiniLogger()) do
       @info "hello" x=4 y=2
       end
[2022-04-29 10:55:19] Info: hello x = 4, y = 2

Additional test cases:
There should be no extra space when there are no keywords present:

julia> with_logger(MiniLogger()) do
       @info "hello"
       end
[2022-04-29 10:55:19] Info: hello

And there should be no extra space when there is no text message:

julia> with_logger(MiniLogger()) do
       @info x=4 y=2
       end
[2022-04-29 10:55:19] Info: x = 4, y = 2

[Arkoniak]

Unfortunately it is impossible to generate last test case, due to the way, how Julia prepares message. It can be seen in default logger too

julia> @info x = 3 y = 1
┌ Info: 3
└   y = 1

First argument always stripped to it's value and considered as message itself. Only way to overcome it, that I can find now, is to add empty string at the beginning of the log string

julia> @info "" x = 3 y = 1
┌ Info:
│   x = 3
└   y = 1

or the same in MiniLoggers.jl

julia> with_logger(MiniLogger()) do
       @info "" x=4 y=2
       end
[2022-04-29 10:55:19] Info: x = 4, y = 2

[cossio]

Thanks for handling this!