Splitting up monolithic file.

[Cohors1316]

Was trying to build a linux info iterator and got annoyed with trying to find things in the monolith. Mostly caused by windows taking up so much space.

Summary of other stuff I touched:

• Created functional loopback tests.
• Swapped out baud maps for std.c.speed_t, which contains baud enums for most OS now.
• Created speed enums for windows, covers every speed available to the other os.
• Change BaudRate to enums.
• Created enum for flushing buffers so it's explicit.
• Created init func to streamline things.

[Cohors1316]

Random note: for whatever reason File.readAll will not return if the bytes remaining are less than the buffer size. Pretty darn sure I had a test that worked correctly with no bytes in the read buffer, in fact I know I did because the buffer was a bunch of nulls I had to fill the buffer with zeros first. Maybe it's a linux vs windows thing.

edit: someone broke the windows read funcs in zig master.

[Cohors1316]

Realized windows is gonna take a lot to fix.