"format" should escape more control characters

[d-torrance]

This still needs a bit more work:

i2 : toJSON "foo\0"

o2 = "foo\0"

i3 : fromJSON oo
stdio:3:8:(3): error: syntax error at token '0', position 5

toJSON "foo\0" should probably instead return "foo\u0000". I think maybe format should just do that for all the control characters except the ones that JSON supports like \n and \t. I'll take a look at some other common standards (Python strings, etc.) and try to make format output things that are as universal as possible.

Originally posted by @d-torrance in #3670 (comment)